diff --git a/build_config/host-debug.rb b/build_config/host-debug.rb
index 600a4d78f..5f1e10c6e 100644
--- a/build_config/host-debug.rb
+++ b/build_config/host-debug.rb
@@ -13,6 +13,9 @@ MRuby::Build.new('host') do |conf|
   # Generate mruby debugger command (require mruby-eval)
   conf.gem :core => "mruby-bin-debugger"
 
+  # Regexp
+  conf.gem :core => "mruby-regexp"
+
   # test
   conf.enable_test
   # bintest
diff --git a/mrbgems/mruby-regexp/include/re_internal.h b/mrbgems/mruby-regexp/include/re_internal.h
new file mode 100644
index 000000000..82ace6461
--- /dev/null
+++ b/mrbgems/mruby-regexp/include/re_internal.h
@@ -0,0 +1,95 @@
+/*
+** re_internal.h - internal definitions for regexp engine
+**
+** See Copyright Notice in mruby.h
+*/
+
+#ifndef MRB_RE_INTERNAL_H
+#define MRB_RE_INTERNAL_H
+
+#include <mruby.h>
+#include <stdint.h>
+
+/* Bytecode instructions for the NFA engine */
+enum re_opcode {
+  RE_CHAR,       /* match literal byte: operand = byte value */
+  RE_ANY,        /* match any character (. without DOTALL) */
+  RE_ANY_NL,     /* match any character including newline (. with DOTALL) */
+  RE_CLASS,      /* match character class: operand = class_id */
+  RE_NCLASS,     /* match negated character class: operand = class_id */
+  RE_MATCH,      /* successful match */
+  RE_JMP,        /* unconditional jump: operand = target offset */
+  RE_SPLIT,      /* fork: operand = target offset (greedy: try next first) */
+  RE_SPLITNG,    /* fork: operand = target offset (non-greedy: try jump first) */
+  RE_SAVE,       /* save capture position: operand = slot number */
+  RE_BOL,        /* assert beginning of line (^) */
+  RE_EOL,        /* assert end of line ($) */
+  RE_BOT,        /* assert beginning of text (\A) */
+  RE_EOT,        /* assert end of text (\z) */
+  RE_EOTNL,     /* assert end of text or before final \n (\Z) */
+  RE_WBOUND,     /* assert word boundary (\b) */
+  RE_NWBOUND,    /* assert non-word boundary (\B) */
+  RE_BACKREF,    /* backreference: operand = group number */
+};
+
+/* Bytecode instruction (4 bytes each for alignment) */
+typedef struct {
+  uint8_t op;
+  uint8_t a;       /* small operand or class id */
+  uint16_t offset;  /* jump target or extended operand */
+} re_inst;
+
+/* Character class bitmap (ASCII range) */
+#define RE_CLASS_BITMAP_SIZE 16  /* 128 bits = 16 bytes for ASCII */
+typedef struct {
+  uint8_t bitmap[RE_CLASS_BITMAP_SIZE];  /* bitmap for 0-127 */
+  mrb_bool negated;
+  mrb_bool utf8_any;  /* match any non-ASCII byte if true */
+} re_charclass;
+
+/* Compiled regexp pattern */
+typedef struct mrb_regexp_pattern {
+  re_inst *code;          /* bytecode array */
+  uint32_t code_len;      /* number of instructions */
+  re_charclass *classes;   /* character class table */
+  uint16_t num_classes;
+  uint16_t num_captures;   /* number of capture groups (including group 0) */
+  uint32_t flags;
+  mrb_bool has_backref;    /* true if pattern uses \1-\9 */
+} mrb_regexp_pattern;
+
+/* Regexp flags */
+#define RE_FLAG_IGNORECASE  1
+#define RE_FLAG_MULTILINE   2  /* ^ and $ match at \n boundaries */
+#define RE_FLAG_DOTALL      4  /* . matches \n (Ruby's /m for dot behavior) */
+
+/* Note: Ruby's /m flag means BOTH multiline anchors AND dotall.
+   Ruby's /i flag is ignorecase. */
+
+/* Step limit for ReDoS protection */
+#ifndef MRB_REGEXP_STEP_LIMIT
+#define MRB_REGEXP_STEP_LIMIT 1000000
+#endif
+
+/* Maximum captures */
+#define RE_MAX_CAPTURES 32
+
+/* Compile a pattern string into bytecode */
+mrb_regexp_pattern* re_compile(mrb_state *mrb, const char *pattern, mrb_int len, uint32_t flags);
+
+/* Free a compiled pattern */
+void re_free(mrb_state *mrb, mrb_regexp_pattern *pat);
+
+/* Execute a match.
+   Returns number of captures filled (0 = no match).
+   captures[2*n] = start, captures[2*n+1] = end for group n. */
+int re_exec(mrb_state *mrb, const mrb_regexp_pattern *pat,
+            const char *str, mrb_int len, mrb_int start,
+            int *captures, int captures_size);
+
+/* UTF-8 helpers */
+int re_utf8_charlen(const char *s, const char *end);
+uint32_t re_utf8_decode(const char *s, int *len);
+mrb_bool re_is_word_char(uint32_t c);
+
+#endif /* MRB_RE_INTERNAL_H */
diff --git a/mrbgems/mruby-regexp/mrbgem.rake b/mrbgems/mruby-regexp/mrbgem.rake
new file mode 100644
index 000000000..c5879908d
--- /dev/null
+++ b/mrbgems/mruby-regexp/mrbgem.rake
@@ -0,0 +1,7 @@
+MRuby::Gem::Specification.new('mruby-regexp') do |spec|
+  spec.license = 'MIT'
+  spec.authors = 'mruby developers'
+  spec.summary = 'Regexp class (built-in NFA engine)'
+
+  spec.add_dependency 'mruby-string-ext', :core => 'mruby-string-ext'
+end
diff --git a/mrbgems/mruby-regexp/mrblib/string_regexp.rb b/mrbgems/mruby-regexp/mrblib/string_regexp.rb
new file mode 100644
index 000000000..28b225ec8
--- /dev/null
+++ b/mrbgems/mruby-regexp/mrblib/string_regexp.rb
@@ -0,0 +1,126 @@
+class String
+  def match(re, pos = 0)
+    re = Regexp.new(re) if re.is_a?(String)
+    re.match(self, pos)
+  end
+
+  def match?(re, pos = 0)
+    re = Regexp.new(re) if re.is_a?(String)
+    re.match?(self, pos)
+  end
+
+  def =~(re)
+    re =~ self
+  end
+
+  def sub(pattern, replacement = nil, &block)
+    pattern = Regexp.new(Regexp.escape(pattern)) if pattern.is_a?(String)
+    md = pattern.match(self)
+    return self.dup unless md
+
+    pre = md.pre_match
+    post = md.post_match
+    if block
+      rep = block.call(md[0]).to_s
+    else
+      rep = replacement.to_s
+      # handle \0, \1, etc. in replacement string
+      rep = rep.gsub(/\\(\d)/) { md[$1.to_i] || "" } if rep.include?("\\")
+    end
+    pre + rep + post
+  end
+
+  def gsub(pattern, replacement = nil, &block)
+    pattern = Regexp.new(Regexp.escape(pattern)) if pattern.is_a?(String)
+    result = ""
+    rest = self
+    while rest.length > 0
+      md = pattern.match(rest)
+      break unless md
+      result += md.pre_match
+      if block
+        result += block.call(md[0]).to_s
+      else
+        rep = replacement.to_s
+        rep = rep.gsub(/\\(\d)/) { md[$1.to_i] || "" } if rep.include?("\\")
+        result += rep
+      end
+      matched_len = md[0].length
+      if matched_len == 0
+        # avoid infinite loop on zero-length match
+        result += rest[0] if rest.length > 0
+        rest = rest[1..-1] || ""
+      else
+        rest = md.post_match
+      end
+    end
+    result + rest
+  end
+
+  def scan(pattern)
+    pattern = Regexp.new(Regexp.escape(pattern)) if pattern.is_a?(String)
+    result = []
+    pos = 0
+    while pos <= self.length
+      md = pattern.match(self, pos)
+      break unless md
+      if md.captures.empty?
+        result << md[0]
+      elsif md.captures.length == 1
+        result << md.captures[0]
+      else
+        result << md.captures
+      end
+      if md[0].length == 0
+        pos = md.end(0) + 1
+      else
+        pos = md.end(0)
+      end
+    end
+    if block_given?
+      result.each { |m| yield m }
+      self
+    else
+      result
+    end
+  end
+
+  def split(pattern = nil, limit = -1)
+    return super if pattern.nil?
+    if pattern.is_a?(String)
+      return super if pattern.length == 1 || !pattern.include?('\\')
+      pattern = Regexp.new(Regexp.escape(pattern))
+    end
+    result = []
+    rest = self
+    count = 0
+    while rest.length > 0
+      if limit > 0 && count >= limit - 1
+        result << rest
+        return result
+      end
+      md = pattern.match(rest)
+      break unless md
+      result << md.pre_match
+      rest = md.post_match
+      count += 1
+      # skip zero-length match at beginning
+      if md[0].length == 0
+        if rest.length > 0
+          result[-1] = result[-1] + rest[0]
+          rest = rest[1..-1] || ""
+        else
+          break
+        end
+      end
+    end
+    result << rest
+    # remove trailing empty strings if no limit
+    if limit < 0
+      while result.length > 0 && result[-1] == ""
+        result.pop
+      end
+    end
+    result
+  end
+end
diff --git a/mrbgems/mruby-regexp/src/re_compile.c b/mrbgems/mruby-regexp/src/re_compile.c
new file mode 100644
index 000000000..0cf9e3928
--- /dev/null
+++ b/mrbgems/mruby-regexp/src/re_compile.c
@@ -0,0 +1,611 @@
+/*
+** re_compile.c - regexp pattern compiler
+**
+** Compiles a regular expression pattern string into bytecode
+** for the NFA execution engine.
+**
+** See Copyright Notice in mruby.h
+*/
+
+#include "re_internal.h"
+#include <mruby/error.h>
+#include <string.h>
+
+/* Compiler state */
+typedef struct {
+  mrb_state *mrb;
+  const char *src;     /* pattern source */
+  const char *src_end;
+  const char *p;       /* current position */
+  re_inst *code;       /* instruction array */
+  uint32_t code_len;
+  uint32_t code_capa;
+  re_charclass *classes;
+  uint16_t num_classes;
+  uint16_t class_capa;
+  uint16_t num_captures;
+  uint32_t flags;
+  mrb_bool has_backref;
+} re_compiler;
+
+static void compile_alt(re_compiler *c);  /* forward */
+
+static void
+compile_error(re_compiler *c, const char *msg)
+{
+  mrb_raisef(c->mrb, mrb_exc_get_id(c->mrb, MRB_SYM(RegexpError)), "%s: /%s/", msg, c->src);
+}
+
+static uint32_t
+emit(re_compiler *c, uint8_t op, uint8_t a, uint16_t offset)
+{
+  if (c->code_len >= c->code_capa) {
+    c->code_capa = c->code_capa ? c->code_capa * 2 : 64;
+    c->code = (re_inst*)mrb_realloc(c->mrb, c->code, sizeof(re_inst) * c->code_capa);
+  }
+  uint32_t pos = c->code_len++;
+  c->code[pos].op = op;
+  c->code[pos].a = a;
+  c->code[pos].offset = offset;
+  return pos;
+}
+
+static void
+patch(re_compiler *c, uint32_t pos, uint16_t offset)
+{
+  c->code[pos].offset = offset;
+}
+
+/* Insert an instruction at position `pos` by shifting code.
+   Adjusts all jump offsets >= pos by +1. */
+static void
+insert_inst(re_compiler *c, uint32_t pos, uint8_t op, uint8_t a, uint16_t offset)
+{
+  emit(c, RE_JMP, 0, 0);  /* grow array */
+  uint32_t len = c->code_len - 1 - pos;
+  memmove(&c->code[pos + 1], &c->code[pos], sizeof(re_inst) * len);
+  c->code[pos].op = op;
+  c->code[pos].a = a;
+  c->code[pos].offset = offset;
+
+  /* fix all jump targets that point at or past the insertion point */
+  for (uint32_t i = 0; i < c->code_len; i++) {
+    if (i == pos) continue;
+    switch (c->code[i].op) {
+    case RE_JMP: case RE_SPLIT: case RE_SPLITNG:
+      if (c->code[i].offset >= pos && c->code[i].offset < 0xffff) {
+        c->code[i].offset++;
+      }
+      break;
+    default:
+      break;
+    }
+  }
+}
+
+static int
+peek(re_compiler *c)
+{
+  if (c->p >= c->src_end) return -1;
+  return (uint8_t)*c->p;
+}
+
+static int
+next_char(re_compiler *c)
+{
+  if (c->p >= c->src_end) return -1;
+  return (uint8_t)*c->p++;
+}
+
+static uint16_t
+add_class(re_compiler *c)
+{
+  if (c->num_classes >= c->class_capa) {
+    c->class_capa = c->class_capa ? c->class_capa * 2 : 8;
+    c->classes = (re_charclass*)mrb_realloc(c->mrb, c->classes, sizeof(re_charclass) * c->class_capa);
+  }
+  uint16_t id = c->num_classes++;
+  memset(&c->classes[id], 0, sizeof(re_charclass));
+  return id;
+}
+
+static void
+class_set_bit(re_charclass *cc, uint8_t ch)
+{
+  if (ch < 128) {
+    cc->bitmap[ch >> 3] |= (1 << (ch & 7));
+  }
+}
+
+static void
+class_set_range(re_charclass *cc, uint8_t lo, uint8_t hi)
+{
+  for (int i = lo; i <= hi; i++) {
+    class_set_bit(cc, (uint8_t)i);
+  }
+}
+
+static void
+class_add_shorthand(re_charclass *cc, int ch)
+{
+  switch (ch) {
+  case 'd':
+    class_set_range(cc, '0', '9');
+    break;
+  case 'D':
+    class_set_range(cc, 0, '0'-1);
+    class_set_range(cc, '9'+1, 127);
+    cc->utf8_any = TRUE;
+    break;
+  case 'w':
+    class_set_range(cc, 'a', 'z');
+    class_set_range(cc, 'A', 'Z');
+    class_set_range(cc, '0', '9');
+    class_set_bit(cc, '_');
+    break;
+  case 'W':
+    for (int i = 0; i < 128; i++) {
+      if (!re_is_word_char(i)) class_set_bit(cc, (uint8_t)i);
+    }
+    cc->utf8_any = TRUE;
+    break;
+  case 's':
+    class_set_bit(cc, ' ');
+    class_set_bit(cc, '\t');
+    class_set_bit(cc, '\n');
+    class_set_bit(cc, '\r');
+    class_set_bit(cc, '\f');
+    class_set_bit(cc, '\v');
+    break;
+  case 'S':
+    for (int i = 0; i < 128; i++) {
+      if (i != ' ' && i != '\t' && i != '\n' && i != '\r' && i != '\f' && i != '\v')
+        class_set_bit(cc, (uint8_t)i);
+    }
+    cc->utf8_any = TRUE;
+    break;
+  }
+}
+
+static int
+parse_escape(re_compiler *c)
+{
+  int ch = next_char(c);
+  if (ch < 0) compile_error(c, "trailing backslash");
+  switch (ch) {
+  case 'n': return '\n';
+  case 't': return '\t';
+  case 'r': return '\r';
+  case 'f': return '\f';
+  case 'v': return '\v';
+  case 'a': return '\a';
+  case 'e': return 0x1b;
+  default: return ch;  /* literal: \., \\, \/, \(, etc. */
+  }
+}
+
+/* Parse [...] character class */
+static void
+compile_charclass(re_compiler *c)
+{
+  uint16_t id = add_class(c);
+  re_charclass *cc = &c->classes[id];
+  mrb_bool negated = FALSE;
+
+  if (peek(c) == '^') {
+    next_char(c);
+    negated = TRUE;
+  }
+
+  mrb_bool first = TRUE;
+  while (peek(c) != ']' || first) {
+    int ch;
+
+    if (peek(c) < 0) compile_error(c, "unterminated character class");
+    first = FALSE;
+
+    if (peek(c) == '\\') {
+      next_char(c);
+      int esc = peek(c);
+      if (esc == 'd' || esc == 'D' || esc == 'w' || esc == 'W' || esc == 's' || esc == 'S') {
+        next_char(c);
+        class_add_shorthand(cc, esc);
+        continue;
+      }
+      ch = parse_escape(c);
+    }
+    else {
+      ch = next_char(c);
+    }
+
+    /* check for range a-z */
+    if (peek(c) == '-' && c->p + 1 < c->src_end && c->p[1] != ']') {
+      next_char(c);  /* skip '-' */
+      int hi;
+      if (peek(c) == '\\') {
+        next_char(c);
+        hi = parse_escape(c);
+      }
+      else {
+        hi = next_char(c);
+      }
+      if (ch < 128 && hi < 128) {
+        class_set_range(cc, (uint8_t)ch, (uint8_t)hi);
+      }
+    }
+    else {
+      if (ch < 128) class_set_bit(cc, (uint8_t)ch);
+    }
+  }
+  next_char(c);  /* skip ']' */
+
+  cc->negated = negated;
+  emit(c, negated ? RE_NCLASS : RE_CLASS, (uint8_t)id, 0);
+}
+
+/* Parse {n}, {n,}, {n,m} quantifier. Returns min,max via pointers. */
+static mrb_bool
+parse_quantifier(re_compiler *c, int *min_out, int *max_out)
+{
+  const char *save = c->p;
+  int min = 0, max = -1;
+
+  while (peek(c) >= '0' && peek(c) <= '9') {
+    min = min * 10 + (next_char(c) - '0');
+  }
+  if (peek(c) == ',') {
+    next_char(c);
+    if (peek(c) >= '0' && peek(c) <= '9') {
+      max = 0;
+      while (peek(c) >= '0' && peek(c) <= '9') {
+        max = max * 10 + (next_char(c) - '0');
+      }
+    }
+    /* else max = -1 (unlimited) */
+  }
+  else {
+    max = min;  /* {n} means exactly n */
+  }
+  if (peek(c) != '}') {
+    c->p = save;  /* not a quantifier, treat { as literal */
+    return FALSE;
+  }
+  next_char(c);  /* skip '}' */
+  *min_out = min;
+  *max_out = max;
+  return TRUE;
+}
+
+/* Compile a single atom (character, class, group, etc.) */
+static void
+compile_atom(re_compiler *c)
+{
+  int ch = peek(c);
+
+  switch (ch) {
+  case '(':
+    {
+      next_char(c);
+      mrb_bool capturing = TRUE;
+
+      if (peek(c) == '?' && c->p + 1 < c->src_end && c->p[1] == ':') {
+        next_char(c); next_char(c);  /* skip ?: */
+        capturing = FALSE;
+      }
+
+      uint16_t group = 0;
+      if (capturing) {
+        if (c->num_captures >= RE_MAX_CAPTURES) {
+          compile_error(c, "too many capture groups");
+        }
+        group = c->num_captures++;
+        emit(c, RE_SAVE, 0, group * 2);
+      }
+
+      compile_alt(c);
+
+      if (peek(c) != ')') compile_error(c, "unmatched '('");
+      next_char(c);
+
+      if (capturing) {
+        emit(c, RE_SAVE, 0, group * 2 + 1);
+      }
+    }
+    break;
+
+  case '[':
+    next_char(c);
+    compile_charclass(c);
+    break;
+
+  case '.':
+    next_char(c);
+    emit(c, (c->flags & RE_FLAG_DOTALL) ? RE_ANY_NL : RE_ANY, 0, 0);
+    break;
+
+  case '^':
+    next_char(c);
+    emit(c, RE_BOL, 0, 0);
+    break;
+
+  case '$':
+    next_char(c);
+    emit(c, RE_EOL, 0, 0);
+    break;
+
+  case '\\':
+    next_char(c);
+    ch = peek(c);
+    if (ch >= '1' && ch <= '9') {
+      next_char(c);
+      emit(c, RE_BACKREF, (uint8_t)(ch - '0'), 0);
+      c->has_backref = TRUE;
+    }
+    else if (ch == 'd' || ch == 'D' || ch == 'w' || ch == 'W' || ch == 's' || ch == 'S') {
+      next_char(c);
+      uint16_t id = add_class(c);
+      class_add_shorthand(&c->classes[id], ch);
+      emit(c, (ch >= 'A' && ch <= 'Z') ? RE_NCLASS : RE_CLASS, (uint8_t)id, 0);
+    }
+    else if (ch == 'A') {
+      next_char(c);
+      emit(c, RE_BOT, 0, 0);
+    }
+    else if (ch == 'z') {
+      next_char(c);
+      emit(c, RE_EOT, 0, 0);
+    }
+    else if (ch == 'Z') {
+      next_char(c);
+      emit(c, RE_EOTNL, 0, 0);
+    }
+    else if (ch == 'b') {
+      next_char(c);
+      emit(c, RE_WBOUND, 0, 0);
+    }
+    else if (ch == 'B') {
+      next_char(c);
+      emit(c, RE_NWBOUND, 0, 0);
+    }
+    else {
+      ch = parse_escape(c);
+      if (c->flags & RE_FLAG_IGNORECASE) {
+        if (ch >= 'A' && ch <= 'Z') {
+          uint16_t id = add_class(c);
+          class_set_bit(&c->classes[id], (uint8_t)ch);
+          class_set_bit(&c->classes[id], (uint8_t)(ch + 32));
+          emit(c, RE_CLASS, (uint8_t)id, 0);
+          break;
+        }
+        else if (ch >= 'a' && ch <= 'z') {
+          uint16_t id = add_class(c);
+          class_set_bit(&c->classes[id], (uint8_t)ch);
+          class_set_bit(&c->classes[id], (uint8_t)(ch - 32));
+          emit(c, RE_CLASS, (uint8_t)id, 0);
+          break;
+        }
+      }
+      emit(c, RE_CHAR, (uint8_t)ch, 0);
+    }
+    break;
+
+  default:
+    if (ch < 0 || ch == ')' || ch == '|' || ch == '*' || ch == '+' || ch == '?' || ch == '{') {
+      return;  /* not an atom */
+    }
+    next_char(c);
+    if ((c->flags & RE_FLAG_IGNORECASE) && ch < 128) {
+      if (ch >= 'A' && ch <= 'Z') {
+        uint16_t id = add_class(c);
+        class_set_bit(&c->classes[id], (uint8_t)ch);
+        class_set_bit(&c->classes[id], (uint8_t)(ch + 32));
+        emit(c, RE_CLASS, (uint8_t)id, 0);
+        break;
+      }
+      else if (ch >= 'a' && ch <= 'z') {
+        uint16_t id = add_class(c);
+        class_set_bit(&c->classes[id], (uint8_t)ch);
+        class_set_bit(&c->classes[id], (uint8_t)(ch - 32));
+        emit(c, RE_CLASS, (uint8_t)id, 0);
+        break;
+      }
+    }
+    emit(c, RE_CHAR, (uint8_t)ch, 0);
+    break;
+  }
+}
+
+/* Compile atom with quantifiers (*, +, ?, {n,m}) */
+static void
+compile_quantified(re_compiler *c)
+{
+  uint32_t start = c->code_len;
+  compile_atom(c);
+  if (c->code_len == start) return;  /* no atom emitted */
+
+  int ch = peek(c);
+  if (ch == '*' || ch == '+' || ch == '?') {
+    next_char(c);
+    mrb_bool nongreedy = (peek(c) == '?');
+    if (nongreedy) next_char(c);
+
+    uint32_t atom_len = c->code_len - start;
+
+    if (ch == '*') {
+      /* e* → L: SPLIT(body, end); body; JMP L; end:
+         SPLIT offset = end (after JMP), patched after JMP is emitted */
+      insert_inst(c, start, nongreedy ? RE_SPLITNG : RE_SPLIT, 0, 0);
+      emit(c, RE_JMP, 0, start);
+      c->code[start].offset = (uint16_t)c->code_len;  /* patch: skip to end */
+    }
+    else if (ch == '+') {
+      /* e+ → body; SPLIT/SPLITNG(start)
+         SPLIT: first=pc+1(end), second=offset(start) → non-greedy
+         SPLITNG: first=offset(start), second=pc+1(end) → greedy */
+      emit(c, nongreedy ? RE_SPLIT : RE_SPLITNG, 0, start);
+    }
+    else { /* ? */
+      /* e? → SPLIT(body, end); body; end: */
+      insert_inst(c, start, nongreedy ? RE_SPLITNG : RE_SPLIT, 0, 0);
+      c->code[start].offset = (uint16_t)c->code_len;  /* patch: skip to end */
+    }
+  }
+  else if (ch == '{') {
+    const char *save = c->p;
+    next_char(c);
+    int min, max;
+    if (!parse_quantifier(c, &min, &max)) {
+      c->p = save;
+      return;  /* not a quantifier */
+    }
+    mrb_bool nongreedy = (peek(c) == '?');
+    if (nongreedy) next_char(c);
+
+    /* For {n,m}: repeat atom min times, then optional (max-min) times */
+    uint32_t atom_end = c->code_len;
+    uint32_t atom_size = atom_end - start;
+
+    /* First, we have one copy already. We need min-1 more mandatory copies. */
+    for (int i = 1; i < min; i++) {
+      for (uint32_t j = 0; j < atom_size; j++) {
+        emit(c, c->code[start + j].op, c->code[start + j].a, c->code[start + j].offset);
+      }
+    }
+    /* Then optional copies */
+    if (max < 0) {
+      /* {n,} = min copies + * */
+      uint32_t loop_start = c->code_len;
+      uint32_t split_pos = emit(c, nongreedy ? RE_SPLITNG : RE_SPLIT, 0, 0);
+      for (uint32_t j = 0; j < atom_size; j++) {
+        emit(c, c->code[start + j].op, c->code[start + j].a, c->code[start + j].offset);
+      }
+      emit(c, RE_JMP, 0, loop_start);
+      patch(c, split_pos, c->code_len);
+    }
+    else {
+      for (int i = min; i < max; i++) {
+        uint32_t split_pos = emit(c, nongreedy ? RE_SPLITNG : RE_SPLIT, 0, 0);
+        for (uint32_t j = 0; j < atom_size; j++) {
+          emit(c, c->code[start + j].op, c->code[start + j].a, c->code[start + j].offset);
+        }
+        patch(c, split_pos, c->code_len);
+      }
+    }
+  }
+}
+
+/* Compile a sequence of quantified atoms */
+static void
+compile_seq(re_compiler *c)
+{
+  while (peek(c) >= 0 && peek(c) != ')' && peek(c) != '|') {
+    compile_quantified(c);
+  }
+}
+
+/* Compile alternation: seq | seq | ... */
+static void
+compile_alt(re_compiler *c)
+{
+  uint32_t alt_start = c->code_len;
+  compile_seq(c);
+
+  if (peek(c) != '|') return;
+
+  /* a|b → SPLIT L1 L2; L1: a; JMP END; L2: b; END:
+     We need to insert SPLIT before already-emitted code for first alt.
+     Strategy: emit JMP after first alt, then for each subsequent alt,
+     insert a SPLIT before it by shifting code. */
+
+  /* Collect all alternatives, then emit SPLIT chain at the end.
+     This avoids insert_inst offset corruption for multi-way alternation. */
+  uint32_t alt_starts[64];  /* start positions of each alternative */
+  int num_alts = 0;
+  alt_starts[num_alts++] = alt_start;
+
+  while (peek(c) == '|') {
+    next_char(c);
+    emit(c, RE_JMP, 0, 0);  /* placeholder: jump to end */
+    alt_starts[num_alts++] = c->code_len;
+    if (num_alts >= 64) compile_error(c, "too many alternatives");
+    compile_seq(c);
+  }
+
+  if (num_alts <= 1) return;  /* shouldn't happen, but safety */
+
+  /* Now insert SPLIT chain before the alternatives.
+     For n alternatives: n-1 SPLIT instructions, each pointing to
+     their respective alternative. */
+  uint32_t split_count = (uint32_t)(num_alts - 1);
+  /* Insert split_count instructions at alt_starts[0] */
+  for (uint32_t i = 0; i < split_count; i++) {
+    insert_inst(c, alt_starts[0], RE_JMP, 0, 0);  /* placeholder */
+    /* adjust all alt_starts by +1 due to insertion */
+    for (int j = 0; j < num_alts; j++) {
+      alt_starts[j]++;
+    }
+  }
+
+  /* Now set up SPLIT chain: each SPLIT tries next instruction or jumps to alt */
+  for (uint32_t i = 0; i < split_count; i++) {
+    uint32_t pos = alt_starts[0] - split_count + i;
+    c->code[pos].op = RE_SPLIT;
+    c->code[pos].a = 0;
+    c->code[pos].offset = (uint16_t)alt_starts[i + 1];
+  }
+
+  /* Patch JMPs (they are right before each alt_starts[1..n-1]) to point to end */
+  uint32_t end = c->code_len;
+  for (int i = 1; i < num_alts; i++) {
+    uint32_t jmp_pos = alt_starts[i] - 1;
+    c->code[jmp_pos].op = RE_JMP;
+    c->code[jmp_pos].offset = (uint16_t)end;
+  }
+}
+
+mrb_regexp_pattern*
+re_compile(mrb_state *mrb, const char *pattern, mrb_int len, uint32_t flags)
+{
+  re_compiler c;
+  memset(&c, 0, sizeof(c));
+  c.mrb = mrb;
+  c.src = pattern;
+  c.src_end = pattern + len;
+  c.p = pattern;
+  c.flags = flags;
+  c.num_captures = 1;  /* group 0 = whole match */
+
+  /* group 0 start */
+  emit(&c, RE_SAVE, 0, 0);
+
+  compile_alt(&c);
+
+  if (c.p < c.src_end) {
+    compile_error(&c, "unmatched ')'");
+  }
+
+  /* group 0 end */
+  emit(&c, RE_SAVE, 0, 1);
+  emit(&c, RE_MATCH, 0, 0);
+
+  mrb_regexp_pattern *pat = (mrb_regexp_pattern*)mrb_malloc(mrb, sizeof(mrb_regexp_pattern));
+  pat->code = c.code;
+  pat->code_len = c.code_len;
+  pat->classes = c.classes;
+  pat->num_classes = c.num_classes;
+  pat->num_captures = c.num_captures;
+  pat->flags = flags;
+  pat->has_backref = c.has_backref;
+
+  return pat;
+}
+
+void
+re_free(mrb_state *mrb, mrb_regexp_pattern *pat)
+{
+  if (pat) {
+    mrb_free(mrb, pat->code);
+    mrb_free(mrb, pat->classes);
+    mrb_free(mrb, pat);
+  }
+}
diff --git a/mrbgems/mruby-regexp/src/re_exec.c b/mrbgems/mruby-regexp/src/re_exec.c
new file mode 100644
index 000000000..aa9deaed0
--- /dev/null
+++ b/mrbgems/mruby-regexp/src/re_exec.c
@@ -0,0 +1,271 @@
+/*
+** re_exec.c - NFA execution engine (Pike VM)
+**
+** Executes compiled regexp bytecode using Thompson/Pike NFA simulation.
+** O(pattern * text) time complexity guarantees ReDoS resistance.
+**
+** See Copyright Notice in mruby.h
+*/
+
+#include "re_internal.h"
+#include <string.h>
+
+/* NFA thread: a position in the bytecode + captured positions */
+typedef struct {
+  uint32_t pc;
+  int captures[RE_MAX_CAPTURES * 2];
+} re_thread;
+
+/* Thread list for NFA simulation */
+typedef struct {
+  re_thread *threads;
+  int count;
+  int capa;
+} re_threadlist;
+
+/* Match result: updated when RE_MATCH is reached during epsilon traversal */
+typedef struct {
+  mrb_bool matched;
+  int captures[RE_MAX_CAPTURES * 2];
+} re_match_result;
+
+static void
+threadlist_init(mrb_state *mrb, re_threadlist *l, int capa)
+{
+  l->threads = (re_thread*)mrb_malloc(mrb, sizeof(re_thread) * capa);
+  l->count = 0;
+  l->capa = capa;
+}
+
+static void
+threadlist_free(mrb_state *mrb, re_threadlist *l)
+{
+  mrb_free(mrb, l->threads);
+}
+
+/* Add a thread, following epsilon transitions (JMP, SPLIT, SAVE, assertions).
+   visited[] prevents adding duplicate threads at the same pc.
+   When RE_MATCH is reached, records in result and does NOT add to thread list. */
+static void
+add_thread(const mrb_regexp_pattern *pat, re_threadlist *list,
+           re_thread t, const char *str, const char *sp, const char *str_end,
+           uint8_t *visited, re_match_result *result)
+{
+  for (;;) {
+    if (t.pc >= pat->code_len) return;
+    if (visited[t.pc]) return;
+    visited[t.pc] = 1;
+
+    re_inst inst = pat->code[t.pc];
+    switch (inst.op) {
+    case RE_JMP:
+      t.pc = inst.offset;
+      continue;
+
+    case RE_SPLIT:
+      /* greedy: try pc+1 first, then jump target */
+      {
+        re_thread t2 = t;
+        t2.pc = inst.offset;
+        add_thread(pat, list, t2, str, sp, str_end, visited, result);
+      }
+      t.pc++;
+      continue;
+
+    case RE_SPLITNG:
+      /* non-greedy: try jump target first, then pc+1 */
+      {
+        re_thread t2 = t;
+        t2.pc = t.pc + 1;
+        add_thread(pat, list, t2, str, sp, str_end, visited, result);
+      }
+      t.pc = inst.offset;
+      continue;
+
+    case RE_SAVE:
+      t.captures[inst.offset] = (int)(sp - str);
+      t.pc++;
+      continue;
+
+    case RE_BOL:
+      if (sp == str || ((pat->flags & RE_FLAG_MULTILINE) && sp > str && sp[-1] == '\n')) {
+        t.pc++; continue;
+      }
+      return;
+
+    case RE_EOL:
+      if (sp == str_end || ((pat->flags & RE_FLAG_MULTILINE) && *sp == '\n')) {
+        t.pc++; continue;
+      }
+      return;
+
+    case RE_BOT:
+      if (sp == str) { t.pc++; continue; }
+      return;
+
+    case RE_EOT:
+      if (sp == str_end) { t.pc++; continue; }
+      return;
+
+    case RE_EOTNL:
+      if (sp == str_end || (sp + 1 == str_end && *sp == '\n')) { t.pc++; continue; }
+      return;
+
+    case RE_WBOUND:
+      {
+        mrb_bool before = (sp > str) && re_is_word_char((uint8_t)sp[-1]);
+        mrb_bool after = (sp < str_end) && re_is_word_char((uint8_t)*sp);
+        if (before != after) { t.pc++; continue; }
+      }
+      return;
+
+    case RE_NWBOUND:
+      {
+        mrb_bool before = (sp > str) && re_is_word_char((uint8_t)sp[-1]);
+        mrb_bool after = (sp < str_end) && re_is_word_char((uint8_t)*sp);
+        if (before == after) { t.pc++; continue; }
+      }
+      return;
+
+    case RE_MATCH:
+      /* match found during epsilon traversal.
+         always update: greedy quantifiers may find longer matches later
+         at the same starting position. thread priority ensures correctness. */
+      if (result) {
+        result->matched = TRUE;
+        memcpy(result->captures, t.captures, sizeof(t.captures));
+      }
+      return;  /* don't add to thread list */
+
+    default:
+      /* consuming instruction: add to thread list */
+      break;
+    }
+    break;
+  }
+
+  /* add to thread list */
+  if (list->count < list->capa) {
+    list->threads[list->count++] = t;
+  }
+}
+
+/* Check if character matches a character class */
+static mrb_bool
+class_match(const re_charclass *cc, uint8_t ch)
+{
+  if (ch >= 128) return cc->utf8_any;
+  return (cc->bitmap[ch >> 3] >> (ch & 7)) & 1;
+}
+
+/* Pike VM: NFA simulation with submatch tracking */
+int
+re_exec(mrb_state *mrb, const mrb_regexp_pattern *pat,
+        const char *str, mrb_int len, mrb_int start,
+        int *captures, int captures_size)
+{
+  const char *sp = str + start;
+  const char *str_end = str + len;
+  int ncap = pat->num_captures * 2;
+
+  int list_capa = (int)pat->code_len * 2 + 16;
+  re_threadlist curr, next;
+  threadlist_init(mrb, &curr, list_capa);
+  threadlist_init(mrb, &next, list_capa);
+
+  uint8_t *visited = (uint8_t*)mrb_calloc(mrb, 1, pat->code_len + 1);
+
+  re_match_result result;
+  result.matched = FALSE;
+  memset(result.captures, -1, sizeof(result.captures));
+
+  for (; sp <= str_end; sp++) {
+    /* Add a new initial thread at current position (unanchored search) */
+    if (!result.matched) {
+      re_thread t0;
+      memset(t0.captures, -1, sizeof(t0.captures));
+      t0.pc = 0;
+      memset(visited, 0, pat->code_len + 1);
+      add_thread(pat, &curr, t0, str, sp, str_end, visited, &result);
+      /* if match found during epsilon traversal (empty pattern), done */
+      if (result.matched && curr.count == 0) break;
+    }
+
+    if (sp >= str_end) break;
+
+    /* Process all current threads against current character */
+    memset(visited, 0, pat->code_len + 1);
+    next.count = 0;
+
+    int ch = (uint8_t)*sp;
+    int advance = re_utf8_charlen(sp, str_end);
+
+    for (int i = 0; i < curr.count; i++) {
+      re_thread *th = &curr.threads[i];
+      if (th->pc >= pat->code_len) continue;
+
+      re_inst inst = pat->code[th->pc];
+      switch (inst.op) {
+      case RE_CHAR:
+        if (ch == inst.a) {
+          th->pc++;
+          add_thread(pat, &next, *th, str, sp + 1, str_end, visited, &result);
+        }
+        break;
+
+      case RE_ANY:
+        if (ch != '\n') {
+          th->pc++;
+          add_thread(pat, &next, *th, str, sp + advance, str_end, visited, &result);
+        }
+        break;
+
+      case RE_ANY_NL:
+        th->pc++;
+        add_thread(pat, &next, *th, str, sp + advance, str_end, visited, &result);
+        break;
+
+      case RE_CLASS:
+        if (class_match(&pat->classes[inst.a], (uint8_t)ch)) {
+          th->pc++;
+          add_thread(pat, &next, *th, str, sp + advance, str_end, visited, &result);
+        }
+        break;
+
+      case RE_NCLASS:
+        if (!class_match(&pat->classes[inst.a], (uint8_t)ch)) {
+          th->pc++;
+          add_thread(pat, &next, *th, str, sp + advance, str_end, visited, &result);
+        }
+        break;
+
+      case RE_BACKREF:
+        /* TODO: backtracking for backreferences */
+        break;
+
+      default:
+        break;
+      }
+    }
+
+    /* swap curr and next */
+    {
+      re_threadlist tmp = curr;
+      curr = next;
+      next = tmp;
+    }
+
+    /* if matched and no more threads, we're done */
+    if (result.matched && curr.count == 0) break;
+  }
+
+  threadlist_free(mrb, &curr);
+  threadlist_free(mrb, &next);
+  mrb_free(mrb, visited);
+
+  if (result.matched && captures) {
+    int copy = ncap < captures_size ? ncap : captures_size;
+    memcpy(captures, result.captures, sizeof(int) * copy);
+  }
+  return result.matched ? (ncap > 0 ? ncap : 1) : 0;
+}
diff --git a/mrbgems/mruby-regexp/src/re_utf8.c b/mrbgems/mruby-regexp/src/re_utf8.c
new file mode 100644
index 000000000..82f22b1bb
--- /dev/null
+++ b/mrbgems/mruby-regexp/src/re_utf8.c
@@ -0,0 +1,76 @@
+/*
+** re_utf8.c - UTF-8 utility functions for regexp engine
+**
+** See Copyright Notice in mruby.h
+*/
+
+#include "re_internal.h"
+
+/* Return byte length of UTF-8 character at s.
+   Returns 1 for invalid sequences (treat as single byte). */
+int
+re_utf8_charlen(const char *s, const char *end)
+{
+  uint8_t c = (uint8_t)*s;
+  int len;
+
+  if (c < 0x80) return 1;
+  else if (c < 0xc0) return 1;  /* invalid continuation */
+  else if (c < 0xe0) len = 2;
+  else if (c < 0xf0) len = 3;
+  else if (c < 0xf8) len = 4;
+  else return 1;  /* invalid */
+
+  if (s + len > end) return 1;  /* truncated */
+  return len;
+}
+
+/* Decode a UTF-8 character and return its codepoint.
+   *len is set to the byte length consumed. */
+uint32_t
+re_utf8_decode(const char *s, int *len)
+{
+  uint8_t c = (uint8_t)s[0];
+  uint32_t cp;
+
+  if (c < 0x80) {
+    *len = 1;
+    return c;
+  }
+  else if (c < 0xc0) {
+    *len = 1;
+    return c;  /* invalid, return as-is */
+  }
+  else if (c < 0xe0) {
+    *len = 2;
+    cp = (c & 0x1f) << 6;
+    cp |= ((uint8_t)s[1] & 0x3f);
+    return cp;
+  }
+  else if (c < 0xf0) {
+    *len = 3;
+    cp = (c & 0x0f) << 12;
+    cp |= ((uint8_t)s[1] & 0x3f) << 6;
+    cp |= ((uint8_t)s[2] & 0x3f);
+    return cp;
+  }
+  else {
+    *len = 4;
+    cp = (c & 0x07) << 18;
+    cp |= ((uint8_t)s[1] & 0x3f) << 12;
+    cp |= ((uint8_t)s[2] & 0x3f) << 6;
+    cp |= ((uint8_t)s[3] & 0x3f);
+    return cp;
+  }
+}
+
+/* Check if character is a "word" character (\w): [a-zA-Z0-9_] */
+mrb_bool
+re_is_word_char(uint32_t c)
+{
+  if (c >= 'a' && c <= 'z') return TRUE;
+  if (c >= 'A' && c <= 'Z') return TRUE;
+  if (c >= '0' && c <= '9') return TRUE;
+  if (c == '_') return TRUE;
+  return FALSE;
+}
diff --git a/mrbgems/mruby-regexp/src/regexp.c b/mrbgems/mruby-regexp/src/regexp.c
new file mode 100644
index 000000000..1c6ec180c
--- /dev/null
+++ b/mrbgems/mruby-regexp/src/regexp.c
@@ -0,0 +1,427 @@
+/*
+** regexp.c - Regexp class and MatchData class
+**
+** See Copyright Notice in mruby.h
+*/
+
+#include <mruby.h>
+#include <mruby/class.h>
+#include <mruby/data.h>
+#include <mruby/string.h>
+#include <mruby/array.h>
+#include <mruby/variable.h>
+#include <mruby/error.h>
+#include "re_internal.h"
+
+#include <string.h>
+
+/* Regexp data type */
+static void regexp_free(mrb_state *mrb, void *ptr) {
+  re_free(mrb, (mrb_regexp_pattern*)ptr);
+}
+
+static const struct mrb_data_type regexp_type = { "Regexp", regexp_free };
+
+/* MatchData */
+typedef struct {
+  mrb_value source;        /* source string */
+  int *captures;           /* capture positions [start0,end0,start1,end1,...] */
+  int num_captures;        /* number of capture groups (including 0) */
+} mrb_match_data;
+
+static void matchdata_free(mrb_state *mrb, void *ptr) {
+  mrb_match_data *md = (mrb_match_data*)ptr;
+  if (md) {
+    mrb_free(mrb, md->captures);
+    mrb_free(mrb, md);
+  }
+}
+
+static const struct mrb_data_type matchdata_type = { "MatchData", matchdata_free };
+
+/* Parse flags from string or integer */
+static uint32_t
+parse_flags(mrb_state *mrb, mrb_value flags_val)
+{
+  uint32_t flags = 0;
+  if (mrb_integer_p(flags_val)) {
+    mrb_int f = mrb_integer(flags_val);
+    if (f & 1) flags |= RE_FLAG_IGNORECASE;
+    if (f & 4) flags |= RE_FLAG_MULTILINE | RE_FLAG_DOTALL;
+    return flags;
+  }
+  if (mrb_string_p(flags_val)) {
+    const char *s = RSTRING_PTR(flags_val);
+    mrb_int len = RSTRING_LEN(flags_val);
+    for (mrb_int i = 0; i < len; i++) {
+      switch (s[i]) {
+      case 'i': flags |= RE_FLAG_IGNORECASE; break;
+      case 'm': flags |= RE_FLAG_MULTILINE | RE_FLAG_DOTALL; break;
+      case 'x': break; /* TODO: extended mode */
+      }
+    }
+    return flags;
+  }
+  if (mrb_test(flags_val)) flags |= RE_FLAG_IGNORECASE;
+  return flags;
+}
+
+/*
+ * Regexp.new(pattern, flags=nil)
+ * Regexp.compile(pattern, flags=nil)
+ */
+static mrb_value
+regexp_init(mrb_state *mrb, mrb_value self)
+{
+  mrb_value pattern;
+  mrb_value flags_val = mrb_nil_value();
+  mrb_regexp_pattern *pat;
+
+  mrb_get_args(mrb, "S|o", &pattern, &flags_val);
+
+  uint32_t flags = parse_flags(mrb, flags_val);
+  pat = re_compile(mrb, RSTRING_PTR(pattern), RSTRING_LEN(pattern), flags);
+
+  DATA_TYPE(self) = &regexp_type;
+  DATA_PTR(self) = pat;
+
+  /* store source for #source and #inspect */
+  mrb_iv_set(mrb, self, mrb_intern_lit(mrb, "@source"), pattern);
+  mrb_iv_set(mrb, self, mrb_intern_lit(mrb, "@flags"), mrb_int_value(mrb, (mrb_int)flags));
+
+  return self;
+}
+
+/* Create MatchData from captures */
+static mrb_value
+create_matchdata(mrb_state *mrb, mrb_value str, int *captures, int ncap)
+{
+  struct RClass *md_class = mrb_class_get(mrb, "MatchData");
+  mrb_match_data *md = (mrb_match_data*)mrb_malloc(mrb, sizeof(mrb_match_data));
+  md->source = str;
+  md->num_captures = ncap / 2;
+  md->captures = (int*)mrb_malloc(mrb, sizeof(int) * ncap);
+  memcpy(md->captures, captures, sizeof(int) * ncap);
+
+  mrb_value obj = mrb_obj_value(mrb_data_object_alloc(mrb, md_class, md, &matchdata_type));
+  /* store in $~ */
+  return obj;
+}
+
+/*
+ * Regexp#match(str, pos=0)
+ */
+static mrb_value
+regexp_match(mrb_state *mrb, mrb_value self)
+{
+  mrb_value str;
+  mrb_int pos = 0;
+  mrb_regexp_pattern *pat;
+
+  mrb_get_args(mrb, "S|i", &str, &pos);
+  pat = DATA_GET_PTR(mrb, self, &regexp_type, mrb_regexp_pattern);
+  if (!pat) mrb_raise(mrb, E_ARGUMENT_ERROR, "uninitialized Regexp");
+
+  int captures[RE_MAX_CAPTURES * 2];
+  memset(captures, -1, sizeof(captures));
+  int ncap = re_exec(mrb, pat, RSTRING_PTR(str), RSTRING_LEN(str), pos,
+                     captures, pat->num_captures * 2);
+
+  if (ncap == 0) return mrb_nil_value();
+
+  return create_matchdata(mrb, str, captures, pat->num_captures * 2);
+}
+
+/*
+ * Regexp#match?(str, pos=0)
+ */
+static mrb_value
+regexp_match_p(mrb_state *mrb, mrb_value self)
+{
+  mrb_value str;
+  mrb_int pos = 0;
+  mrb_regexp_pattern *pat;
+
+  mrb_get_args(mrb, "S|i", &str, &pos);
+  pat = DATA_GET_PTR(mrb, self, &regexp_type, mrb_regexp_pattern);
+  if (!pat) mrb_raise(mrb, E_ARGUMENT_ERROR, "uninitialized Regexp");
+
+  int ncap = re_exec(mrb, pat, RSTRING_PTR(str), RSTRING_LEN(str), pos, NULL, 0);
+  return mrb_bool_value(ncap > 0);
+}
+
+/*
+ * Regexp#=~(str)
+ */
+static mrb_value
+regexp_match_op(mrb_state *mrb, mrb_value self)
+{
+  mrb_value str;
+  mrb_regexp_pattern *pat;
+
+  mrb_get_args(mrb, "o", &str);
+  if (mrb_nil_p(str)) return mrb_nil_value();
+  mrb_ensure_string_type(mrb, str);
+
+  pat = DATA_GET_PTR(mrb, self, &regexp_type, mrb_regexp_pattern);
+  if (!pat) mrb_raise(mrb, E_ARGUMENT_ERROR, "uninitialized Regexp");
+
+  int captures[RE_MAX_CAPTURES * 2];
+  memset(captures, -1, sizeof(captures));
+  int ncap = re_exec(mrb, pat, RSTRING_PTR(str), RSTRING_LEN(str), 0,
+                     captures, pat->num_captures * 2);
+
+  if (ncap == 0) return mrb_nil_value();
+  return mrb_int_value(mrb, captures[0]);
+}
+
+/*
+ * Regexp#===(str)
+ */
+static mrb_value
+regexp_case_match(mrb_state *mrb, mrb_value self)
+{
+  mrb_value str;
+  mrb_regexp_pattern *pat;
+
+  mrb_get_args(mrb, "o", &str);
+  if (!mrb_string_p(str)) return mrb_false_value();
+
+  pat = DATA_GET_PTR(mrb, self, &regexp_type, mrb_regexp_pattern);
+  if (!pat) return mrb_false_value();
+
+  int ncap = re_exec(mrb, pat, RSTRING_PTR(str), RSTRING_LEN(str), 0, NULL, 0);
+  return mrb_bool_value(ncap > 0);
+}
+
+/*
+ * Regexp#source
+ */
+static mrb_value
+regexp_source(mrb_state *mrb, mrb_value self)
+{
+  return mrb_iv_get(mrb, self, mrb_intern_lit(mrb, "@source"));
+}
+
+/*
+ * Regexp#inspect
+ */
+static mrb_value
+regexp_inspect(mrb_state *mrb, mrb_value self)
+{
+  mrb_value src = mrb_iv_get(mrb, self, mrb_intern_lit(mrb, "@source"));
+  mrb_value flags_val = mrb_iv_get(mrb, self, mrb_intern_lit(mrb, "@flags"));
+  uint32_t flags = mrb_nil_p(flags_val) ? 0 : (uint32_t)mrb_integer(flags_val);
+
+  mrb_value result = mrb_str_new_lit(mrb, "/");
+  mrb_str_cat_str(mrb, result, src);
+  mrb_str_cat_lit(mrb, result, "/");
+  if (flags & RE_FLAG_IGNORECASE) mrb_str_cat_lit(mrb, result, "i");
+  if (flags & RE_FLAG_MULTILINE) mrb_str_cat_lit(mrb, result, "m");
+  return result;
+}
+
+/*
+ * Regexp.escape(str)
+ */
+static mrb_value
+regexp_escape(mrb_state *mrb, mrb_value self)
+{
+  mrb_value str;
+  mrb_get_args(mrb, "S", &str);
+
+  const char *s = RSTRING_PTR(str);
+  mrb_int len = RSTRING_LEN(str);
+  mrb_value result = mrb_str_new_capa(mrb, len + len / 4);
+
+  for (mrb_int i = 0; i < len; i++) {
+    char c = s[i];
+    switch (c) {
+    case '\\': case '.': case '*': case '+': case '?': case '|':
+    case '(': case ')': case '[': case ']': case '{': case '}':
+    case '^': case '$':
+      mrb_str_cat_lit(mrb, result, "\\");
+      /* fall through */
+    default:
+      mrb_str_cat(mrb, result, &c, 1);
+      break;
+    }
+  }
+  return result;
+}
+
+/* --- MatchData methods --- */
+
+/*
+ * MatchData#[](n)
+ */
+static mrb_value
+matchdata_aref(mrb_state *mrb, mrb_value self)
+{
+  mrb_int idx;
+  mrb_get_args(mrb, "i", &idx);
+
+  mrb_match_data *md = DATA_GET_PTR(mrb, self, &matchdata_type, mrb_match_data);
+  if (!md) return mrb_nil_value();
+
+  if (idx < 0 || idx >= md->num_captures) return mrb_nil_value();
+  int start = md->captures[idx * 2];
+  int end = md->captures[idx * 2 + 1];
+  if (start < 0) return mrb_nil_value();
+
+  return mrb_str_substr(mrb, md->source, start, end - start);
+}
+
+/*
+ * MatchData#captures
+ */
+static mrb_value
+matchdata_captures(mrb_state *mrb, mrb_value self)
+{
+  mrb_match_data *md = DATA_GET_PTR(mrb, self, &matchdata_type, mrb_match_data);
+  if (!md) return mrb_ary_new(mrb);
+
+  mrb_value ary = mrb_ary_new_capa(mrb, md->num_captures - 1);
+  for (int i = 1; i < md->num_captures; i++) {
+    int start = md->captures[i * 2];
+    int end = md->captures[i * 2 + 1];
+    if (start < 0) {
+      mrb_ary_push(mrb, ary, mrb_nil_value());
+    }
+    else {
+      mrb_ary_push(mrb, ary, mrb_str_substr(mrb, md->source, start, end - start));
+    }
+  }
+  return ary;
+}
+
+/*
+ * MatchData#to_a
+ */
+static mrb_value
+matchdata_to_a(mrb_state *mrb, mrb_value self)
+{
+  mrb_match_data *md = DATA_GET_PTR(mrb, self, &matchdata_type, mrb_match_data);
+  if (!md) return mrb_ary_new(mrb);
+
+  mrb_value ary = mrb_ary_new_capa(mrb, md->num_captures);
+  for (int i = 0; i < md->num_captures; i++) {
+    int start = md->captures[i * 2];
+    int end = md->captures[i * 2 + 1];
+    if (start < 0) {
+      mrb_ary_push(mrb, ary, mrb_nil_value());
+    }
+    else {
+      mrb_ary_push(mrb, ary, mrb_str_substr(mrb, md->source, start, end - start));
+    }
+  }
+  return ary;
+}
+
+/*
+ * MatchData#begin(n) / MatchData#end(n)
+ */
+static mrb_value
+matchdata_begin(mrb_state *mrb, mrb_value self)
+{
+  mrb_int idx;
+  mrb_get_args(mrb, "i", &idx);
+
+  mrb_match_data *md = DATA_GET_PTR(mrb, self, &matchdata_type, mrb_match_data);
+  if (!md || idx < 0 || idx >= md->num_captures) return mrb_nil_value();
+  int pos = md->captures[idx * 2];
+  if (pos < 0) return mrb_nil_value();
+  return mrb_int_value(mrb, pos);
+}
+
+static mrb_value
+matchdata_end(mrb_state *mrb, mrb_value self)
+{
+  mrb_int idx;
+  mrb_get_args(mrb, "i", &idx);
+
+  mrb_match_data *md = DATA_GET_PTR(mrb, self, &matchdata_type, mrb_match_data);
+  if (!md || idx < 0 || idx >= md->num_captures) return mrb_nil_value();
+  int pos = md->captures[idx * 2 + 1];
+  if (pos < 0) return mrb_nil_value();
+  return mrb_int_value(mrb, pos);
+}
+
+/*
+ * MatchData#pre_match / #post_match
+ */
+static mrb_value
+matchdata_pre(mrb_state *mrb, mrb_value self)
+{
+  mrb_match_data *md = DATA_GET_PTR(mrb, self, &matchdata_type, mrb_match_data);
+  if (!md || md->captures[0] < 0) return mrb_nil_value();
+  return mrb_str_substr(mrb, md->source, 0, md->captures[0]);
+}
+
+static mrb_value
+matchdata_post(mrb_state *mrb, mrb_value self)
+{
+  mrb_match_data *md = DATA_GET_PTR(mrb, self, &matchdata_type, mrb_match_data);
+  if (!md || md->captures[1] < 0) return mrb_nil_value();
+  int pos = md->captures[1];
+  return mrb_str_substr(mrb, md->source, pos, RSTRING_LEN(md->source) - pos);
+}
+
+/*
+ * MatchData#length / #size
+ */
+static mrb_value
+matchdata_length(mrb_state *mrb, mrb_value self)
+{
+  mrb_match_data *md = DATA_GET_PTR(mrb, self, &matchdata_type, mrb_match_data);
+  if (!md) return mrb_fixnum_value(0);
+  return mrb_fixnum_value(md->num_captures);
+}
+
+/* --- Gem init --- */
+
+void
+mrb_mruby_regexp_gem_init(mrb_state *mrb)
+{
+  struct RClass *re = mrb_define_class(mrb, "Regexp", mrb->object_class);
+  MRB_SET_INSTANCE_TT(re, MRB_TT_CDATA);
+
+  /* Constants */
+  mrb_define_const(mrb, re, "IGNORECASE", mrb_fixnum_value(1));
+  mrb_define_const(mrb, re, "EXTENDED", mrb_fixnum_value(2));
+  mrb_define_const(mrb, re, "MULTILINE", mrb_fixnum_value(4));
+
+  /* Class methods */
+  mrb_define_method(mrb, re, "initialize", regexp_init, MRB_ARGS_ARG(1, 2));
+  mrb_define_class_method(mrb, re, "compile", regexp_init, MRB_ARGS_ARG(1, 2));
+  mrb_define_class_method(mrb, re, "escape", regexp_escape, MRB_ARGS_REQ(1));
+  mrb_define_class_method(mrb, re, "quote", regexp_escape, MRB_ARGS_REQ(1));
+
+  /* Instance methods */
+  mrb_define_method(mrb, re, "match", regexp_match, MRB_ARGS_ARG(1, 1));
+  mrb_define_method(mrb, re, "match?", regexp_match_p, MRB_ARGS_ARG(1, 1));
+  mrb_define_method(mrb, re, "=~", regexp_match_op, MRB_ARGS_REQ(1));
+  mrb_define_method(mrb, re, "===", regexp_case_match, MRB_ARGS_REQ(1));
+  mrb_define_method(mrb, re, "source", regexp_source, MRB_ARGS_NONE());
+  mrb_define_method(mrb, re, "inspect", regexp_inspect, MRB_ARGS_NONE());
+  mrb_define_method(mrb, re, "to_s", regexp_inspect, MRB_ARGS_NONE());
+
+  /* MatchData class */
+  struct RClass *md = mrb_define_class(mrb, "MatchData", mrb->object_class);
+  MRB_SET_INSTANCE_TT(md, MRB_TT_CDATA);
+
+  mrb_define_method(mrb, md, "[]", matchdata_aref, MRB_ARGS_REQ(1));
+  mrb_define_method(mrb, md, "captures", matchdata_captures, MRB_ARGS_NONE());
+  mrb_define_method(mrb, md, "to_a", matchdata_to_a, MRB_ARGS_NONE());
+  mrb_define_method(mrb, md, "length", matchdata_length, MRB_ARGS_NONE());
+  mrb_define_method(mrb, md, "size", matchdata_length, MRB_ARGS_NONE());
+  mrb_define_method(mrb, md, "begin", matchdata_begin, MRB_ARGS_REQ(1));
+  mrb_define_method(mrb, md, "end", matchdata_end, MRB_ARGS_REQ(1));
+  mrb_define_method(mrb, md, "pre_match", matchdata_pre, MRB_ARGS_NONE());
+  mrb_define_method(mrb, md, "post_match", matchdata_post, MRB_ARGS_NONE());
+}
+
+void
+mrb_mruby_regexp_gem_final(mrb_state *mrb)
+{
+}
diff --git a/mrbgems/mruby-regexp/test/regexp.rb b/mrbgems/mruby-regexp/test/regexp.rb
new file mode 100644
index 000000000..45ee42051
--- /dev/null
+++ b/mrbgems/mruby-regexp/test/regexp.rb
@@ -0,0 +1,141 @@
+assert("Regexp.new") do
+  re = Regexp.new("abc")
+  assert_kind_of Regexp, re
+end
+
+assert("Regexp#match - simple") do
+  re = Regexp.new("abc")
+  md = re.match("xabcy")
+  assert_kind_of MatchData, md
+  assert_equal "abc", md[0]
+end
+
+assert("Regexp#match - no match") do
+  re = Regexp.new("xyz")
+  assert_nil re.match("abc")
+end
+
+assert("Regexp#match?") do
+  re = Regexp.new("abc")
+  assert_true re.match?("xabcy")
+  assert_false re.match?("xyz")
+end
+
+assert("Regexp#=~") do
+  re = Regexp.new("bc")
+  assert_equal 1, re =~ "abcd"
+  assert_nil re =~ "xyz"
+end
+
+assert("Regexp#===") do
+  re = Regexp.new("abc")
+  assert_true re === "abc"
+  assert_false re === "xyz"
+end
+
+assert("Regexp - character class") do
+  re = Regexp.new("[a-z]+")
+  md = re.match("123abc456")
+  assert_equal "abc", md[0]
+end
+
+assert("Regexp - dot") do
+  re = Regexp.new("a.c")
+  assert_true re.match?("abc")
+  assert_true re.match?("axc")
+  assert_false re.match?("ac")
+end
+
+assert("Regexp - alternation") do
+  re = Regexp.new("cat|dog")
+  assert_equal "cat", re.match("I have a cat")[0]
+  assert_equal "dog", re.match("I have a dog")[0]
+end
+
+assert("Regexp - quantifiers") do
+  assert_equal "aaa", Regexp.new("a+").match("aaa")[0]
+  assert_equal "", Regexp.new("a*").match("bbb")[0]
+  assert_equal "ab", Regexp.new("ab?").match("ab")[0]
+  assert_equal "a", Regexp.new("ab?").match("ac")[0]
+end
+
+assert("Regexp - captures") do
+  re = Regexp.new("(\\w+)@(\\w+)")
+  md = re.match("user@host")
+  assert_equal "user@host", md[0]
+  assert_equal "user", md[1]
+  assert_equal "host", md[2]
+end
+
+assert("Regexp - \\d \\w \\s") do
+  assert_true Regexp.new("\\d+").match?("123")
+  assert_true Regexp.new("\\w+").match?("abc_123")
+  assert_true Regexp.new("\\s+").match?("  ")
+  assert_false Regexp.new("\\d+").match?("abc")
+end
+
+assert("Regexp - anchors") do
+  assert_true Regexp.new("^abc").match?("abc")
+  assert_false Regexp.new("^abc").match?("xabc")
+  assert_true Regexp.new("abc$").match?("abc")
+  assert_false Regexp.new("abc$").match?("abcx")
+end
+
+assert("Regexp - case insensitive") do
+  re = Regexp.new("abc", Regexp::IGNORECASE)
+  assert_true re.match?("ABC")
+  assert_true re.match?("Abc")
+end
+
+assert("Regexp - repetition {n,m}") do
+  assert_equal "aaa", Regexp.new("a{3}").match("aaaa")[0]
+  assert_equal "aa", Regexp.new("a{2,3}").match("aa")[0]
+  assert_equal "aaa", Regexp.new("a{2,3}").match("aaaa")[0]
+end
+
+assert("MatchData#captures") do
+  re = Regexp.new("(a)(b)(c)")
+  md = re.match("abc")
+  assert_equal ["a", "b", "c"], md.captures
+end
+
+assert("MatchData#pre_match / #post_match") do
+  re = Regexp.new("bc")
+  md = re.match("abcde")
+  assert_equal "a", md.pre_match
+  assert_equal "de", md.post_match
+end
+
+assert("MatchData#begin / #end") do
+  re = Regexp.new("bc")
+  md = re.match("abcde")
+  assert_equal 1, md.begin(0)
+  assert_equal 3, md.end(0)
+end
+
+assert("Regexp.escape") do
+  assert_equal "a\\.b\\*c", Regexp.escape("a.b*c")
+end
+
+assert("Regexp#inspect") do
+  re = Regexp.new("abc", Regexp::IGNORECASE)
+  assert_equal "/abc/i", re.inspect
+end
+
+assert("String#match") do
+  md = "hello world".match(Regexp.new("(\\w+)\\s(\\w+)"))
+  assert_equal "hello", md[1]
+  assert_equal "world", md[2]
+end
+
+assert("String#sub") do
+  assert_equal "hXllo", "hello".sub(Regexp.new("e"), "X")
+end
+
+assert("String#gsub") do
+  assert_equal "h-ll-", "hello".gsub(Regexp.new("[eo]"), "-")
+end
+
+assert("String#scan") do
+  assert_equal ["1", "2", "3"], "a1b2c3".scan(Regexp.new("\\d"))
+end