The doctrine of ‘indirect effect’ requires national courts, as organs of the Member State responsible for fulfilment of EU obligations, to interpret domestic law consistently with directives. This doctrine achieves indirectly, through the technique of judicial interpretation of domestic law, the result obtainable through the doctrine of direct effect of directives.
Indirect effect can thus be seen both as an addition to and as the corollary of the doctrine of direct effect. In the case of provisions of directives having direct effect, national courts must disregard domestic law where there is a conflict between the directive and domestic law. In the case of a directive lacking direct effect, the national courts must make every effort to interpret domestic law consistently with the directive.
The doctrine of indirect effect is of vital importance to the enforcement of EU rights against private persons (horizontal direct effect). As directives only have vertical direct effect in claims based on directives against private persons, domestic law may be the only legal basis for a claim. The domestic court is obliged to exert itself to ensure that domestic law is interpreted consistently with the EU directive. However, this result is obtainable as far as the national law is not wholly inconsistent with EU law.