Dark Ideas is the first book of its kind to show how ideas have transformed violent extremism over the past six decades. Certain violent jihadi and neo-Nazi innovations have now become accepted practices by groups and individuals, yet they are rarely examined from this perspective. This book comparatively examines some of these strategic and tactical ideas in context. Innovations such as how to weaponize thoughts, create new forms of violence, or shift targets advance terrorism studies into the realm of violent extremist doctrine. Each chapter examines the most influential violent jihadi or neo-Nazi ideologue behind an innovation, the context from which it originated, and how it transitioned from idea to action. The author concludes with some recommendations for policymakers and experts in the field.