diff --git a/src/main/java/groovy/transform/Monadic.java b/src/main/java/groovy/transform/Monadic.java
new file mode 100644
index 00000000000..c9f5736304f
--- /dev/null
+++ b/src/main/java/groovy/transform/Monadic.java
@@ -0,0 +1,52 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements. See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership. The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License. You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied. See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+package groovy.transform;
+
+import org.apache.groovy.lang.annotation.Incubating;
+
+import java.lang.annotation.Documented;
+import java.lang.annotation.ElementType;
+import java.lang.annotation.Retention;
+import java.lang.annotation.RetentionPolicy;
+import java.lang.annotation.Target;
+
+/**
+ * Marks a type as participating in monadic comprehensions (the {@code DO} macro).
+ * Optional members declare the bind/map method names when they diverge from the
+ * structural convention ({@code flatMap}/{@code map}). When both are omitted, the
+ * annotation merely opts the type in and the structural defaults apply.
+ *
+ * Modelled on {@link groovy.transform.Reducer}: a pure marker, read by tooling,
+ * with no AST transformation. The runtime dispatcher and the type checker match
+ * this annotation by simple name ({@code Monadic}), exactly as
+ * {@code groovy.typecheckers.CombinerChecker} matches {@code @Reducer}/{@code @Associative}.
+ *
+ * @since 6.0.0
+ */
+@Documented
+@Incubating
+@Target(ElementType.TYPE)
+@Retention(RetentionPolicy.RUNTIME)
+public @interface Monadic {
+ /** The flatMap-shaped bind method name. Empty means the structural default {@code flatMap}. */
+ String bind() default "";
+
+ /** The map method name. Empty means the structural default {@code map}. */
+ String map() default "";
+}
diff --git a/src/main/java/org/apache/groovy/runtime/Comprehensions.java b/src/main/java/org/apache/groovy/runtime/Comprehensions.java
new file mode 100644
index 00000000000..78b85efc73d
--- /dev/null
+++ b/src/main/java/org/apache/groovy/runtime/Comprehensions.java
@@ -0,0 +1,190 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements. See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership. The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License. You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied. See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+package org.apache.groovy.runtime;
+
+import groovy.lang.Closure;
+import org.apache.groovy.lang.annotation.Incubating;
+import org.codehaus.groovy.runtime.DefaultGroovyMethods;
+import org.codehaus.groovy.runtime.InvokerHelper;
+
+import java.lang.annotation.Annotation;
+import java.lang.reflect.Method;
+import java.util.function.Function;
+
+/**
+ * Runtime bind/map dispatcher for monadic comprehensions — the emit target
+ * of the {@code DO} macro.
+ *
+ * The macro runs at {@code SEMANTIC_ANALYSIS}, before type checking, so it
+ * cannot know the carrier's bind-method name and cannot emit it directly. Instead it
+ * emits {@code Comprehensions.bind(carrier) { x -> ... }} calls; this class resolves
+ * the carrier-specific method at runtime (dynamic Groovy), while the
+ * {@code groovy.typecheckers.MonadicChecker} type-checking extension specialises this
+ * one signature under {@code @CompileStatic}.
+ *
+ * This is runtime support invoked from generated bytecode, hence its placement in
+ * core alongside the rest of the Groovy runtime; the {@code DO} macro and the type
+ * checker are compile-time only and remain in their optional modules.
+ *
+ * Participation is resolved first-match-wins:
+ *
+ * - standard allow-list ({@link MonadicCarrierRegistry});
+ * - structural ({@code flatMap}/{@code map} present);
+ * - {@code @Monadic} opt-in (matched by simple name; honours {@code bind}/{@code map} overrides).
+ *
+ * A configured marker interface is a further opt-in mechanism that is not yet
+ * implemented.
+ *
+ * Surface generosity: the carrier's bind method may accept a {@link Function} or a
+ * {@code Closure}; the closure is adapted to whichever the target declares. Monad
+ * laws are not enforced — structural participation, algebraic-law obligation
+ * on the implementer (the {@code @Reducer}/{@code @Associative} treatment).
+ *
+ * @since 6.0.0
+ */
+@Incubating
+public final class Comprehensions {
+
+ private Comprehensions() {}
+
+ /** Bind (flatMap-shaped): {@code carrier.(x -> fn(x))} where {@code fn} yields the same carrier. */
+ public static Object bind(Object carrier, Closure fn) {
+ return dispatch(carrier, fn, true);
+ }
+
+ /** Map: {@code carrier.