This thesis is a socio-historical analysis of the ways in which the myth of the Internal Threatening Other influences national politics and culture and inter-ethnic relations between the majority group (the dominant ethnic nation) and the minority (perceived as the foremost Threatening Other). The case-study under examination is that of the Polish Jewish minority vis-a vis the Polish ethnic majority from the rise of fully-fledged Polish exclusivist ethno-nationalism in the 1880s up to the year 1968 which marks a final watershed in the history of Polish Jews - the purge and exile of most of its post-war remnants. The thesis examines the multi-faceted structure of the myth, its persistence and adaptability to different historical and socio-political conditions, and the variety of its uses in political culture: such as the purification of the state and dominant nation from the influence and presence of an ethnic minority; its role in anti-minority violence; in raising national cohesion; and in the delegitimisation of political enemies. The thesis is divided into six chapters. The first chapter explores some theoretical issues which underlie the analysis of the thesis; the second chapter examines the roots of the myth, its nascent pre-1880 forms and its development as a fully-fledged myth from the 1880s up to 1939; the third chapter examines the impact of the myth on the rationalisation and justification of anti-Jewish violence between 1918 and 1939: the fourth chapter examines the presence of the myth within the underground state and society during the Second World War; the fifth chapter examines the presence of the myth within political elites and non-elites in the early post-war Communist period 1945-1948 and the last chapter examines the use of the myth by the Communist state between 1967 and 1968.