AbstractWhat explains change in third party dispute settlement in regional international organizations (RIOs)? This paper confronts this question by exploring the extent to which different explanations of institutional change hold in the context of trade RIO third party dispute settlement. The paper considers the role of three variables in explaining dispute settlement reform: the balance of power, the level of trade interdependence between member states and the nature of the organization's founding contract. A truth table reveals that although power and trade interdependence can explain some cases of institutional reform, the nature of the organization's founding contract is the strongest predictor for change in dispute settlement. Nevertheless, the analysis shows that not all cases can be explained, and that the influence of other institutions on the same issue can also play an important role. A case study of the Latin American Free Trade Association illustrates the importance of the institutional environment in which the RIO operates for institutional reform.