Islam and Christianity are the two dominant religious traditions in Nigeria, each shaping the social, cultural, and political landscapes of the country. This chapter examines the historical trajectory of these religions in northern Nigeria, the introduction of foreign religious ideologies, and the emergence of extreme religious movements. Northern Nigeria, predominantly Muslim with significant Christian minorities, illustrates the intersection of religion, ethnicity, and socioeconomic factors in the development of religious extremism. The analysis highlights the historical coexistence of Sufi orders and early Christian missions, the disruptive impact of imported ideologies such as Pentecostalism, Salafism, and Shi’ism, and the socioeconomic drivers that facilitate radicalization. This chapter argues that understanding extremism in northern Nigeria requires a multilayered approach considering historical, religious, and sociopolitical dimensions, offering lessons for managing religious pluralism in other multi-faith societies.