This chapter provides an introduction to economic and monetary union (EMU). It describes the key components of EMU and what happens when countries join. EMU was the result of decades of collaboration and learning, which have been subdivided here into three periods: 1969–91, taking us from the European Council’s first agreement to set up EMU to Maastricht, when the European Council included EMU in the Treaty on European Union (TEU); 1992–2002, from when plans for EMU were being developed to the irrevocable fixing of exchange rates; and 2002 onwards, once EMU had been established, and euro banknotes and coins were circulating in member states. Next, the chapter reviews various theoretical explanations, both economic and political, accounting for why EMU was created and looks at some criticisms of EMU. Finally, the chapter discusses how EMU has fared under the global financial crisis and the sovereign debt crisis. These crises brought to the fore various imperfections in the design of EMU. This section discusses what changes have been made since 2009 to address those flaws and at what we may expect in the years to come.