This study examines the dynamics of religious terrorism in Bangladesh and its implications for internal security. Terrorism motivated by religious ideology has become a critical concern, undermining social cohesion and state resilience (Arefin & Ritu, 2025; Mostofa, 2021). The research investigates the origins of militancy, the structures and activities of Islamist extremist groups, and their strategies between 1999 and 2017. It also considers the drivers of radicalization and the financial mechanisms that sustain these networks (Rone et al., 2025). Methodologically, the study employs qualitative content analysis of secondary sources, supplemented by expert interviews and testimonies from conflict-prone areas (Huda & Mojumder, 2025). The findings identify Jama’atul Mujahideen Bangladesh (JMB), Jagrata Muslim Janata Bangladesh (JMJB), Harkat-ul-Jihad-al-Islami Bangladesh (HUJI-B), and Hizb ut-Tahrir (HT) as the principal extremist groups. These organizations have mobilized thousands of adherents, operated under shifting identities, and maintained transnational linkages with networks in Pakistan, India, and Gulf states (Hasan & Parvez, 2021). The study contributes to scholarship on terrorism and security by highlighting the persistence, adaptability, and international dimensions of Islamist militancy in Bangladesh (Mostofa, 2021; Rone et al., 2025).