(4)This Directive aims to provide for an internal market for AIFMs and a harmonised and stringent regulatory and supervisory framework for the activities within the Union of all AIFMs, including those which have their registered office in a Member State (EU AIFMs) and those which have their registered office in a third country (non-EU AIFMs). As the practical consequences and possible difficulties resulting from a harmonised regulatory framework and an internal market for non-EU AIFMs performing management and/or marketing activities within the Union and EU AIFMs managing non-EU alternative investment funds (AIFs), are uncertain and difficult to predict due to the lack of previous experience in this regard, a review mechanism should be provided for. It is intended that, after a transitional period of 2 years, a harmonised passport regime become applicable to non-EU AIFMs performing management and/or marketing activities within the Union and EU AIFMs managing non-EU AIFs after the entry into force of a delegated act by the Commission in this regard. It is intended that the harmonised regime, during a further transitional period of 3 years, co-exist with the national regimes of the Member States subject to certain minimum harmonised conditions. After that 3-year period of co-existence, it is intended that the national regimes be brought to an end on the entry into force of a further delegated act by the Commission.