Based on seven years of original research, this book contains one of the most detailed and comprehensive assessments of 'home-grown' Islamist terrorism (HGIT) in the US and UK to date. Beginning with an examination of the development of militant networks during the 1980s and 1990s, it traces the origins of HGIT and highlights the significance of these early experiences in different countries for shaping the future trajectory of the threat. The book also examines the range of motivations for violent jihad in the West, suggesting a composite theoretical model that specifies three 'necessary' conditions for involvement and challenges popular explanations for differential rates of terrorism which emphasize socioeconomic factors. The book analyzes the background and operational activities of nearly 800 American and British jihadis who mobilized between 1980 and September 11th 2013, including factors such as mental health, education, processes of radicalization, leadership, use of the Internet, sources of funding and links to foreign terrorist organizations. This analysis is then complemented with an examination of how these individuals have been dealt with by the respective security services. From the first proponents of 'global jihad' to the recent wave of volunteers inspired by events in the Middle East, this book provides an extensive yet lucid analysis of one of the greatest security concerns facing America and Great Britain today. 'Home-Grown' Jihad challenges existing studies on a number of key issues and expands our understanding of HGIT. It will be invaluable to academics, practitioners and policymakers alike.