ISIS formed through a combination of a rise in violent extremist ideologies demonstrated on September 11, 2001; the invasion of Iraq; and the Syrian Civil War. ISIS is possibly the most important conflict group and phenomena of the last half century, and understanding its source and success is crucial to functioning in the world today. This book provides insight into ISIS from its beginnings to the present, through coverage of its people, organizations, and operations. The book begins with an overview of ISIS, which provides context for each of the reference entries that follow. The introductory material also includes entries on the causes and consequences of the conflict between ISIS and the West. The book contains more than 100 reference entries on general and specific topics ranging from key leaders to major terrorist attacks and affiliated organizations. It also includes a carefully curated selection of primary sources that come from a variety of sources including national-level strategy documents, presidential addresses, and ISIS itself. The book concludes with a detailed chronology and annotated bibliography.