Research into the British Union of Fascists (BUF) has treated antisemitism largely as an artificial addition to the party's programme, forced upon it by various circumstances. Scholars have thus focused almost exclusively on its causes and implications, rather than the antisemitism itself: the forms that it took, the ways in which it was expressed, and its relationship to the party's ideology. Through comprehensive analysis of the BUF's discourse, as well as of the discussions that took place within the party, this thesis reveals that anti-Jewish sentiment was, in fact, openly expressed at the very highest levels of the movement from the outset and, moreover, that it formed an integral and authentic aspect of its doctrine. This reflected its central position in the fascist philosophy of the BUF's founder and leader, Oswald Mosley, who was not, as is often argued, a reluctant antisemite. In fact, he played the principal role in the formulation and promulgation of this aspect of policy. More broadly, Mosley's antisemitism is shown to be indicative of ‘generic' fascism's exclusionary ultranationalism, which dictates intolerance of distinctive out-groups deemed incompatible with the fascist vision of a pure, homogenous society, and whose removal is regarded as a necessary prerequisite to bring about national rebirth. This did not, however, mean that the BUF's position on the Jewish question was at all imitative, and this study will demonstrate the extent to which it was founded upon longstanding native traditions of anti-Jewish thought. With regard to the second subject of this thesis, Jewish responses to the BUF, historical accounts have tended to focus only on the most visible forms of activity, and above all the type of confrontational anti-fascism that was favoured by many young, working-class Jews, particularly in London's East End. By exploring a much wider range of Jewish analyses and actions, this study presents a more nuanced and variegated picture. In doing so, it demonstrates that, rather than exacerbating divisions within Britain's heterogeneous Jewish community, the threat of fascism actually drew it closer together in its defence, bringing to the surface a shared sense of Anglo-Jewish identity. Finally, although revealing the breadth and effectiveness of Jewish opposition to British fascism, this study refutes the widely held notion that Jewish actions played any part in pushing the BUF and Mosley towards an antisemitic position.