Why does mediation, as a form of international conflict management, succeed or fail? This question, central to the field of mediation research since its inception, is the raison d'etre of this thesis. The assignments emanating from this question are thus: firstly, and most importantly, to discover those factors and conditions within the mediation relationship which are the central determinants of mediation success or failure; secondly, to reach an understanding of how to define and classify the concepts of success and failure; thirdly, to devise a framework which will give a sense of order to the milieu of actors, issues, perceptions and behaviour present in a conflict/ mediation case; and fourthly, to discover a research method which will allow the integration of a theoretical foundation with a rigorous empirical approach. Initially, attention is given to understanding mediation, its necessity, and the different methods available for analysing it as a phenomenon of social science research. This done, the focus shifts to the "dependent variable" of the thesis, namely mediation outcome, and how (a) success and failure can be defined and classified, and (b) how an outcome can be understood as the end result of a framework of four variables which represent the mediation relationship. Once constructed, this framework provides the grounding for the construction of fifteen hypotheses, drawn from the theoretical literature, which link certain factors and conditions in the framework to mediation success or failure. These hypotheses are then examined for validity, using a correlates of mediation dataset, constructed through the systematic empirical method from actual cases of international mediation. The analysis is initially bivariate, but then moves to a more complex multivariate approach. It is found that there are many significant influences upon mediation outcome, but that the central determinant of whether mediation succeeds or fails is the interrelationship between three factors: the complexity of the dispute, the relationship between the disputants prior to the conflict, and the environment where the mediation takes place. These findings are reintegrated into the theoretical understanding of mediation, and the thesis concludes with some of the practical lessons for mediators provided by the analysis of the study.