The popular conception of John Calvin today is as a divisive figure within Christianity, who vehemently opposed some beliefs while demanding rigid acceptance of others. In this thesis, I intend to investigate the accuracy of that conception by exploring how Calvin approached ecumenicalism theologically and practically. This will cover Calvin's understanding of the Church, his cooperation and disagreements with other Christians, and evaluate what Calvin might contribute to an ecclesiology useful for the Church today. Calvin has gained a poor reputation in modern times both for participation in historical events, including the execution of Servetus, and also for the association of Calvin with the Calvinism that arose after his death in the Netherlands and then in the United States. Calvin is associated with a strong anti-secularism, rigid doctrine (particularly arising out of five point Calvinism), exclusive claims with strictly delineated in and out groups, and ultimately with conservative Christians who are frequently perceived as theocratic far right-wingers. These perceptions stand somewhat, although not fully, in contrast to the very human John Calvin, whose work was frequently designed to build up the Christian Church.