Across the globe, government intelligence agencies play a vital role in protecting their nations from external and internal threats, such as terrorism, espionage, and the spread of weapons of mass destruction. Intelligence agencies also safeguard the economic well-being of their nation states against foreign threats, and support their native law enforcement agencies in detecting and preventing serious crime. A necessary security measure during peacetime as much as during wartime, government intelligence agencies recruit and train some of the finest minds available and conduct high-risk and sometimes life-threatening work on behalf of national security interests. Every day, the agencies and offices of organizations such as the CIA, MI5 in the United Kingdom, the German BND, and the Israeli security service, Mossad, provide important information to the decision makers who manage the nation's strategic interests -- political, economic, and military. Intelligence offices can forewarn governments of impending crises, offer advance knowledge of long-term dangers, and safeguard public security against the threats from terrorists, drug traffickers, and international arms dealers. Government Intelligence Agencies describes the key intelligence agencies in the world, touches on their unique histories, and explains the role that they currently play and the different ways that they contribute to defense and security.