This handbook provides an empirically rich analysis of referendums in Europe from the end of the Second World War to the present. It addresses a range of perennial theoretical and legal questions that face policy-makers when they offer citizens the chance to take or influence decisions by referendum, not least whether to accept the 'will of the people'. Taking a multi-disciplinary approach, drawing on historical, philosophical and political science perspectives, the book includes a contextual section on the history of referendums, the theoretical questions underpinning their use, and on constitutional and legal questions about the use of referendums. The empirical sections are divided into those referendums that focus on domestic issues, such as constitutional matters or questions of social policy, and those related to the European Union, including membership referendums and treaty ratification.