Despite its ubiquity and importance as a means of managing international conflict, mediation has only recently begun to be studied in a systematic manner. This article utilizes an original dataset of international disputes and mediation efforts occurring in the 1945-89 period to assess the character of international mediation and to examine the contextual and process variables which affect mediation outcomes. These variables are classed under four categories: (1) the nature of the disputing parties, (2) the nature of the dispute itself, (3) the identity and characteristics of the mediator, and (4) the strategies and tactics which the mediator employs. In this study, a preliminary analysis is undertaken to determine the nature and degree to which the variables in each of these categories affect mediation outcomes. The results indicate that dispute intensity, mediator strategies and dispute issues exert the greatest influence on the effectiveness of international mediation. A complex of other factors, including the timing of entry into mediation, the power disparity between the disputants and the nature of the disputants' former relations also demonstrate an effect, though somewhat weaker, on mediation outcomes. The article presents conclusions on the effectiveness of international mediation and points the way for more much-needed empirical work in this area.