The scope of powers of international institutions has always been surrounded by a sense of ambiguity. This has its source in the nature of the two main legal tools with which to construct powers; the doctrines of attributed/conferred powers and implied powers. This book illustrates the function of the two doctrines in a discourse on powers. Special attention is also paid to the move to a constitutional vocabulary as a way of transcending the dichotomy at the heart of diverging constructions of powers. Constitutionalization claims, the book argues, can be reproductions of different images of the proper extent of powers. The book is a reminder of the political nature of any construction of powers of international institutions.