This reference is essential reading for anyone attempting to understand modern terrorism by studying the arc of terrorism throughout history, from anarchists to Al Qaeda, ISIS, and beyond. As the rise of ISIS demonstrates, terrorist groups continue to destabilize vital regions around the world. This book features a series of introductory essays addressing how terrorism has evolved, spanning centuries to focus ultimately on the advent of modern terrorism, which has taken place from 1968 to the present. It discusses the emerging challenges presented by the proliferation of violent non-state actors, including Al Qaeda and ISIS. In addition, it explores exactly what has motivated terrorists and speculates as to how terrorism may continue to evolve. The core of Terrorism: The Essential Reference Guide comprises A-Z entries on terrorist organizations, major terrorist attacks, and prominent terrorist leaders. The work concludes with a carefully selected group of primary source documents essential to understanding the contemporary terrorist landscape and a detailed timeline that will help readers to place significant terrorism-related events in their proper context.