Crime and criminal law arguably constitute omnipresent topics in our society. Issues of criminal justice and criminal policy often feature prominently in political discussions and election campaigns. Citizens demand security from their governments and criminal law seems one suitable tool for the task of providing it. This chapter introduces the reader to criminal law by considering its main functions, the rationale behind making something a criminal offence, and its justifications. It offers a careful analysis of the main structure of criminal law across jurisdictions and of the elements required for criminal liability. At the same time, this chapter shows the reader how criminal law is also a tool to protect human rights: it does so by studying procedural safeguards such as the presumption of innocence.