This chapter assesses the doctrine of direct effect across the various sources of European law, starting with the direct effect of the European Treaties. The EU Treaties, as primary law, also envisage the adoption of European secondary law. This secondary law may take various forms. These forms are constitutionally defined in Article 288 TFEU, which sets out the Union's legal instruments. The provision acknowledges three binding legal instruments—regulations, directives, and decisions—and two non-binding instruments. While regulations and decisions were considered Union acts that directly establish legal norms, directives appeared to be designed as indirect forms of legislation. Sadly, Article 288 TFEU is incomplete, for it only mentions the Union's internal instruments. A fourth binding instrument indeed needs to be ‘read into’ the list: international agreements. Union agreements are not only binding upon the institutions of the Union, but also ‘on its Member States’. The chapter then analyses the doctrine of direct effects for international agreements.