This chapter introduces economic and monetary union (EMU), describingthe key components of EMU and what happens when countries join. EMU was the result of decades of collaboration and learning, divided here into three periods: 1969–91, from the agreement to creation to its inclusion in the Treaty on European Union (TEU); 1992–2002, from having the plans for EMU to the irrevocable fixing of exchange rates; and 2002 onwards, with EMU established and euro banknotes and coins circulating in member states. The chapter reviews various theoretical explanations, both economic and political, for the creation of EMU and considers some criticisms of EMU. The chapter discusses how EMU has fared under the global financial crisis, the sovereign debt crisis, and the COVID-19 pandemic. These crises highlighted various imperfections in the design of EMU and provided opportunities for further development. This chapter discusses changes made since 2009 to address those flaws and what may be yet to come.