This chapter draws on theoretical debates within fascism studies, and uses Colin Campbell’s concept of the cultic milieu, to analyse British and American forms of neo-Nazi conspiracy theories. After examining how Nazi conspiracy theories were constructed in Hitler’s Main Kampf, as well as by fringe groups supportive of Nazism such as the Imperial Fascist League, the chapter focuses on their role in 1960s forms of neo-Nazism, such as the Wold Union of National Socialists, and in the ideas of key figures such as George Lincoln Rockwell and Colin Jordan. It then examines how they developed in American Christian Identity literature, as well as in the ideas of William Pierce and David Lane. British examples discussed include the League of St George, Nick Griffin and Combat 18. The chapter concludes by arguing that anti-Semitic conspiracy theories are used widely in neo-Nazi contexts to evoke a sense of faith in a higher cause, and to frame activism as an oppositional and revolutionary alternative to mainstream worldviews.