Written for the general reader as well as the professional, this succinct but comprehensive work examines the hybrid nature of the two violent extremist movements threatening the United States: Islamist extremism and white nationalism. Scholarship as well as popular discourse on terrorism often focuses disproportionately on specific groups without paying sufficient attention to the ideology that motivates them. This book emphasizes understanding and countering the ideology that fuels extremism over preoccupation with specific organizations such as Al Qaeda or ISIS. It sets contemporary terrorist threats in perspective, avoiding fear-mongering and political rhetoric. The book examines the nature of violent extremism today in all its forms, including lone wolves and cyber threats. Focusing on the threats posed by both international and domestic terrorism, it analyzes each in depth as a multidimensional hybrid phenomenon: each threat exists as an ideology, as distinct groups espousing that ideology, and as a network of followers. Short, easy-to-read chapters take readers through the subject matter in a clear, methodical manner. Written in an accessible style by an author who has studied terrorism for more than 30 years and provided extensive media coverage on the subject, the work is a valuable addition to the literature on violent extremism.