diff --git a/test/ruby/test_thread.rb b/test/ruby/test_thread.rb
index f7b33c3..2579fdf 100644
--- a/test/ruby/test_thread.rb
+++ b/test/ruby/test_thread.rb
@@ -708,4 +708,18 @@ class TestThreadGroup < Test::Unit::TestCase
     end
     assert_in_delta(t1 - t0, 1, 1)
   end
+
+  def test_join
+    thgrp = ThreadGroup.new
+
+    thgrp.add(t = Thread.new{ sleep })
+
+    t0 = Time.now.to_f
+    assert_nil(thgrp.join(1))
+    t1 = Time.now.to_f
+    assert_in_delta(t1 - t0, 1, 1)
+
+  ensure
+    t.kill if t
+  end
 end
diff --git a/thread.c b/thread.c
index 55ba49d..05a4f19 100644
--- a/thread.c
+++ b/thread.c
@@ -3139,6 +3139,61 @@ thgroup_list(VALUE group)
     return ary;
 }
 
+struct thgroup_join_params {
+    double limit;
+    VALUE group;
+};
+
+static int
+thgroup_join_i(st_data_t key, st_data_t value, st_data_t data)
+{
+    VALUE thread = (VALUE)key;
+    rb_thread_t *th;
+    struct thgroup_join_params *args = (struct thgroup_join_params *)data;
+    double delay = args->limit;
+
+    GetThreadPtr(thread, th);
+    if (th->thgroup == args->group) {
+	if (delay != DELAY_INFTY) delay -= timeofday();
+	if (NIL_P(thread_join(th, delay))) {
+	    args->group = Qnil;
+	    return ST_STOP;
+	}
+    }
+    return ST_CONTINUE;
+}
+
+/*
+ * call-seq:
+ *    thgrp.join -> thgrp
+ *    thgrp.join(limit) -> thgrp or nil
+ *
+ * The calling thread will suspend execution until threads in the receiving
+ * <code>ThreadGroup</code> exit or until <i>limit</i> seconds have passed.
+ * If the time limit expires, <code>nil</code> will be returned, otherwise
+ * <i>thgrp</i> is returned.
+ *
+ */
+
+static VALUE
+thgroup_join(int argc, VALUE *argv, VALUE self)
+{
+    VALUE limit;
+    struct thgroup_join_params param;
+
+    rb_scan_args(argc, argv, "01", &limit);
+
+    if (!NIL_P(limit)) {
+	param.limit = timeofday() + rb_num2dbl(limit);
+    } else {
+	param.limit = DELAY_INFTY;
+    }
+
+    param.group = self;
+
+    st_foreach(GET_THREAD()->vm->living_threads, thgroup_join_i, (st_data_t) & param);
+    return param.group;
+}
 
 /*
  *  call-seq:
@@ -4622,6 +4677,7 @@ Init_Thread(void)
     rb_define_method(cThGroup, "enclose", thgroup_enclose, 0);
     rb_define_method(cThGroup, "enclosed?", thgroup_enclosed_p, 0);
     rb_define_method(cThGroup, "add", thgroup_add, 1);
+    rb_define_method(cThGroup, "join", thgroup_join, -1);
 
     {
 	th->thgroup = th->vm->thgroup_default = rb_obj_alloc(cThGroup);