The ability of a piece of European Union (EU) legislation to be enforced by an individual in a court of a member state. A provision of EU law may be capable of direct effect if it is clear and precise, unconditional and does not give the member states substantial discretion in its application.

Direct effect may be vertical (that is, the EU legislation can be enforced against the state or an emanation of the state, such as a nationalised industry or privatised utility) or horizontal (that is, it may be enforced against another individual). EU treaty provisions, regulations and decisions are capable of both vertical and horizontal direct effect. Directives can generally only have vertical direct effect. For a directive to have direct effect, there is a further requirement that the time limit for implementation by member states has expired.

Direct effect is related to, but different from, the concept of direct applicability. See also Indirect effect.

For further details, see Practice note, EU law essentials: Direct effect.