This chapter describes how the common agricultural policy (CAP) works and how the policy has changed during its fifty-year existence. It introduces the key actors involved in the policy process and their interests and explains why CAP reform tends to be difficult to make. The chapter also includes a critical discussion on the concept of policy change and an explanation of the factors which are considered decisive in facilitating reform. It focuses on important questions that remain and which the scientific literature so far has not, or only partially, engaged with. The chapter discusses the challenges the CAP is facing and how these are likely to affect future policies and debates, as well as the continued importance of the CAP in the European Union (EU). The aims of the CAP are enshrined in Article 39 of the Treaty on the European Economic Community and remain unchanged in Article 39 of the Treaty on the Functioning of the EU.