This thesis explores the history of Christianity and conversion to it in 16th and 17th Century Japan. It argues that conversion is a complex phenomenon which happened for a variety of reasons. Furthermore, it argues that due to the political context and limitations acting upon the mission, the majority of conversions in 16th and 17th Century Japan lacked an element of epistemological change (classically understood). The first chapter explores theories of conversion suggesting that conversion in 16th and 17th Century Japan included sorts of religious change not usually encapsulated in the term conversion including adhesion, communal and forced conversion. Moreover, it argues that contextual factors are the most important factors in religious change. The second chapter explores political context contending that it was the political environment of Japan that ultimately decided whether conversion was possible. This chapter charts the evolution of the Japanese context as it became more hostile toward Christianity. In the third chapter, the context of the mission is explored. It is argued that limitations acting upon the mission shaped post-conversion faith, so that changes to practice and ritual rather than belief became the mark of a successful conversion. The fourth chapter explores methods of conversion, the factors influencing it, and post-conversion faith more directly. It argues that Christianity spread primarily through social networks, but that conversion was also influenced by economic incentive, other realworld benefits, and Christianity's perceived efficacy. Building on Chapter Three, the final chapter also seeks to illustrate that the missionaries were not successful in their attempts to spur epistemological change or instil a detailed knowledge of theology or doctrine amongst their converts.