This Working Paper examines the indirect effect of international treaty law on domestic legal orders. The question whether domestic courts should attribute indirect effect to international treaty law is pursued from a normative perspective as well as from the perspectives of international law and domestic constitutional law. Against this backdrop, the different forms and methods of attributing indirect effect to international agreements are explored, including in particular agreement-consistent interpretation and other forms of substantive indirect effect, procedural indirect effect, and factual indirect effect. The above points are illustrated, in particular, by reference to the indirect effect of WTO law in relation to the domestic legal orders of the EU and the US.