diff --git a/src/Updux.js b/src/Updux.js
index 1a84745..18bdd7d 100644
--- a/src/Updux.js
+++ b/src/Updux.js
@@ -4,7 +4,7 @@ import { createStore as reduxCreateStore, applyMiddleware } from 'redux';
 
 import { buildSelectors } from './selectors.js';
 import { buildUpreducer } from './upreducer.js';
-import { buildMiddleware } from './middleware.js';
+import { buildMiddleware, augmentMiddlewareApi } from './middleware.js';
 import { action, isActionGen } from './actions.js';
 
 /**
@@ -21,6 +21,7 @@ export class Updux {
     #config = {};
     #selectors = {};
     #effects = [];
+    #localReactions = [];
 
     constructor(config = {}) {
         this.#config = config;
@@ -49,6 +50,8 @@ export class Updux {
         } else if (R.isObject(config.effects)) {
             this.#effects = Object.entries(config.effects);
         }
+
+        this.#localReactions = config.reactions ?? [];
     }
 
     #addSubduxActions(_slice, subdux) {
@@ -171,7 +174,7 @@ export class Updux {
             };
         }
 
-        //this.subscribeAll(store);
+        this.subscribeAll(store);
 
         return store;
     }
@@ -179,6 +182,67 @@ export class Updux {
     addEffect(action, effect) {
         this.#effects = [...this.#effects, [action, effect]];
     }
+
+    addReaction( reaction ) {
+        this.#localReactions = [ ...this.#localReactions, reaction ]
+    }
+
+    subscribeTo(store, subscription) {
+        const localStore = augmentMiddlewareApi(
+            {
+                ...store,
+                subscribe: (subscriber) =>
+                    this.subscribeTo(store, subscriber), // TODO not sure
+            },
+            this.actions,
+            this.selectors
+        );
+
+        const subscriber = subscription(localStore);
+
+        let previous;
+
+        const memoSub = () => {
+            const state = store.getState();
+            if (state === previous) return;
+            let p = previous;
+            previous = state;
+            subscriber(state, p, unsub);
+        };
+
+        let ret = store.subscribe(memoSub);
+        const unsub = typeof ret === 'function' ? ret : ret.unsub;
+        return {
+            unsub,
+            subscriberMemoized: memoSub,
+            subscriber,
+        };
+    }
+
+    subscribeAll(store) {
+        let results = this.#localReactions.map((sub) =>
+            this.subscribeTo(store, sub)
+        );
+
+        for (const subdux in this.#subduxes) {
+            if (subdux !== '*') {
+                const localStore = {
+                    ...store,
+                    getState: () => store.getState()[subdux],
+                };
+                results.push(this.#subduxes[subdux].subscribeAll(localStore));
+            }
+        }
+
+        return {
+            unsub: () => results.forEach(({ unsub }) => unsub()),
+            subscriberMemoized: () =>
+                results.forEach(({ subscriberMemoized}) => subscriberMemoized()),
+            subscriber: () =>
+                results.forEach(({ subscriber }) => subscriber()
+                ),
+        };
+    }
 }
 
 export const dux = (config) => new Updux(config);
diff --git a/src/reactions.test.js b/src/reactions.test.js
new file mode 100644
index 0000000..225b2c7
--- /dev/null
+++ b/src/reactions.test.js
@@ -0,0 +1,50 @@
+import { test, expect, vi } from 'vitest';
+
+import { Updux } from './Updux.js';
+
+test('basic reactions', async () => {
+    const spyA = vi.fn();
+    const spyB = vi.fn();
+    const foo = new Updux({
+        initial: { i: 0 },
+        reactions: [() => spyA],
+        actions: { inc: null },
+        mutations: {
+            inc: () => (state) => ({ ...state, i: state.i + 1 }),
+        },
+    });
+
+    foo.addReaction((api) => spyB);
+
+    const store = foo.createStore();
+    store.dispatch.inc();
+
+    expect(spyA).toHaveBeenCalledOnce();
+    expect(spyB).toHaveBeenCalledOnce();
+});
+
+test('subduxes reactions', async () => {
+    const spyA = vi.fn();
+    const spyB = vi.fn();
+    const foo = new Updux({
+        subduxes: {
+            a: new Updux({
+                initial: 1,
+                reactions: [() => state => spyA(state)],
+                actions: { inc: null },
+                mutations: {
+                    inc: () => (state) => state + 1,
+                },
+            }),
+            b: new Updux({ initial: 10, reactions: [() => spyB] }),
+        },
+    });
+
+    const store = foo.createStore();
+    store.dispatch.inc();
+    store.dispatch.inc();
+
+    expect(spyA).toHaveBeenCalledTimes(2);
+    expect(spyA).toHaveBeenCalledWith(3)
+    expect(spyB).toHaveBeenCalledOnce(); // the original inc initialized the state
+});