This introduction presents an overview of the key concepts discussed in the subsequent chapters of this book. The book provides a discussion of the mainstream understanding of integration, which tends to see the evolution of the European project in the 20th century as a progression of ‘fits and starts’ along a generally linear path forward, yet always prone to crisis or setback. It explains what gendering the European Union (EU) and EU politics means and entails and which key and cross-cutting questions and perspectives. The book explores the history of integration from 1955 to 2005 based on four phases of social policy. It traces the roots of gender equality in the EU by analysing why and how the equal pay Article 119 was included in the European Economic Community Treaty’s social chapter as early as 1957 – agreed on by an all-male group of diplomats.