Departure from the European Union obviously carries with it micro- and macro-economic effects. Only one country has so far left the union (the UK) but others may choose to do so in the future. As a general rule, prediction is not predictive; circumstances and contexts apply. The terms on which a state might leave matter. Nevertheless, there are things which all governments and voters contemplating such a move might bear in mind. The EU is a customs union and contains a single market. A customs union, by definition, creates one tariff on imports around the zone, and a single market ensures smooth trade, a common baseline of standards and regulations, and the free movement of capital, products, goods and services, people, and investment. Any state which left such an arrangement would, even with a comprehensive trade deal, become a third party. It could no longer influence the tariff decisions of the bloc after a transition period, and would without a deal have to pay the import...