Terrorism is a very old type of violence to which dissatisfied people or groups have often resorted over the centuries, causing enormous loss of life and property. Numerous studies have explored various aspects of the phenomenon of terrorism; however, due to the lack of reliable systematic information, the secrecy and dangerousness of terrorist groups terrorism research has relied on perceptions rather than facts about terrorists and terrorist organizations. This EMPIRICAL study aimed to overcome these limitations of terrorism research and contribute to the field by focusing on terrorist recruitment, because the continuation of terrorist activity depends on new recruits and surviving members. Central to this research was the following question: What selection criteria are used by terrorist groups when recruiting new members? The recruitment dynamics of two terrorist groups were examined by using UNIQUE DATA SOURCES and methods. The policy implications that were suggested in this book will shed light on prevention strategies of practitioners and future research of academicians in their effort for a safer world.