This article proposes a theory of legitimacy tailored to international courts and tribunals. In Part II of this paper, the article defines an "international adjudicative body" as a dispute resolution mechanism - also called a "court" or "tribunal" - which decides disputes between litigants, at least one of whom must be a state, and comments on this definitional choice. The analysis in this article is limited only to adjudicative bodies where states are involved as litigants because a different set of legitimacy-influencing factors may be present when only private parties are involved. Next, it lays out a theory of legitimacy specifically for international adjudicative bodies, and distinguishes from prior theoretical approaches, particularly those reliant on "legal legitimacy" alone. Borrowing, in part, from Daniel Bodansky and others, the article defines a "legitimate" international adjudicative body as one whose authority is perceived as justified.

The article identifies three factors which influence the perception of justified authority. These factors include (A) the fair and unbiased nature of the adjudicative body, (B) commitment to the underlying normative regime that the body is interpreting and applying, and (C) the body's transparency and relationship to other democratic values. The three categories are deduced or drawn from state practice as embodied in treaty provisions giving rise to or regulating a cross-section of six international adjudicative bodies - what states actually require before consenting to a court's jurisdiction - as well as legal and political science literature on legitimacy, and logic. It is not the purpose of this article to provide empirical support for these hypotheses, but rather to propose a framework for thinking about legitimacy for future debate and possible empirical testing.