From references to secret agents in The Art of War in 400 B.C.E. to the Bush administration's ongoing War on Terrorism, espionage has always been an essential part of state security policies. This illustrated encyclopedia traces the fascinating stories of spies, intelligence, and counterintelligence throughout history, both internationally and in the United States. Written specifically for students and general readers by scholars, former intelligence officers, and other experts, Encyclopedia of Intelligence and Counterintelligence provides a unique background perspective for viewing history and current events. In easy-to-understand, non-technical language, it explains how espionage works as a function of national policy; traces the roots of national security; profiles key intelligence leaders, agents, and double-agents; discusses intelligence concepts and techniques; and profiles the security organizations and intelligence history and policies of nations around the world. As a special feature, the set also includes forewords by former CIA Director Robert M. Gates and former KGB Major General Oleg Kalugin that help clarify the evolution of intelligence and counterintelligence and their crucial roles in world affairs today.