jonestetc already explained the gist of it - combineReducers expects vanilla javascript objects, not Immutable ones; you can find an example Immutable-compatible implementation here: <a href="https:&#x2F;&#x2F;github.com&#x2F;gajus&#x2F;redux-immutable" rel="nofollow">https:&#x2F;&#x2F;github.com&#x2F;gajus&#x2F;redux-immutable</a><p>We don&#x27;t use it though, it&#x27;s really easy to just create your own version and use that and preferred to have one less dependency.