For nearly two decades, violence by armed groups has posed the most significant threat to peace and security in Nigeria. While the nature of violence perpetrated by armed groups varies by location and time, attacks by Boko Haram Terrorists (BHTs) have caused widespread human and material devastation in Nigeria's northeast and the Lake Chad region. This chapter critically examines the threat posed by the BHT to Nigeria, with a focus on the background, evolution, and activities of emergent factional groups—Jama’atu Ahlus Sunna Lidda’wati Wal Jihad (JAS), Ansaru al-Musulmina fi Bilad al-Sudan (Ansaru), and the Islamic State West African Province (ISWAP). It evaluates the diversity and effectiveness of counterterrorism measures taken against these factions. It contends that despite suffering military defeats and internal divisions, the Boko Haram insurgency reflects both shifts and continuities in Nigeria’s terrorism landscape. The chapter concludes by emphasising the need for the government to enhance transparency, professionalism, and accountability of state security forces, while also addressing the root causes that stimulate and fuel Boko Haram recruitment and radicalisation.