The Schengen Area allows citizens of participating countries to cross each others' borders without border checks (European Commission, Newsweek, European Council on Foreign Relations). Some EU member states do not participate, but so far no country that has joined the area has subsequently withdrawn. A list of Schengen states can be found here. Recommended Questions: Will more than 1 million refugees and migrants arrive in Europe by sea in 2016? Will a majority of voters in Britain's upcoming referendum elect to remain in the European Union?