For a variety of reasons numerous treaties establishing free trade zones as well as other bilateral and regional economic integration agreements have been successfully concluded or are currently under negotiation, among them more recently also emerging so-called “mega-regionals”, occasionally also referred to as “super-RTAs”. The author explores different possibilities of co-existence of such agreements, one of the main issues being whether a state can be at the same time a member of a customs union and a party to an agreement on a free trade area with a third state.