This chapter examines the forms and sources of European Union (EU) law. It describes the nature of the EU legal system and discusses the classification of various elements of EU law, which include institutional laws, procedural laws, and substantive laws. It explains that the Treaty on European Union (TEU) and the Treaty on the Functioning of the European Union (TFEU) are the principal sources of law for the Union. Other sources include regulations, Directives, procedural requirements, and international agreements and conventions. This chapter also discusses the contribution of the European Court of Justice (CJEU) to the sources of EU law.