This chapter outlines a new research agenda on the consequences of legitimacy for the effectiveness of global governance institutions. The chapter sets the stage for systematic investigation of this issue by disaggregating consequences into empirically observable components and by outlining a research strategy to study these different impacts. Specifically, the chapter highlights four sequential types of consequences, relating to: (a) the resources committed to an institution; (b) the scale of policy output produced by an institution; (c) the actor compliance with an institution’s policies; and (d) the problem-solving effectiveness of the institution. The chapter illustrates the empirical fruitfulness of new quantitative measurements of legitimacy crisis, and argues for its usefulness to test effects of legitimacy in global governance.