The dropping of atomic bombs on Hiroshima and Nagasaki in World War II inaugurated a new era in world history, the atomic age. After the war, the Soviet Union, eager to develop the same military capabilities as those demonstrated by the United States, soon rivaled the U.S. as an atomic and nuclear superpower. Faced by the possibility of destruction by nuclear weapons, the nations of the world expressed a keen interest in preventing their proliferation and use, and in ensuring that atomic and nuclear energy sources would be used for peaceful purposes. The International Atomic Energy Agency (IAEA) was established in 1957 as a United Nations agency dedicated to promoting the peaceful uses of atomic and nuclear energy, and also to developing safeguards against the conversion of atomic and nuclear energy from peaceful to military use. When the Nuclear Non-Proliferation Treaty was concluded in 1968, the IAEA was designated as the agency responsible for the inspection of nuclear facilities and for ensuring that countries that signed the treaty were in compliance with its provisions. This article examines the origins of the IAEA and its continuing importance, and describes the activities of the agency in four countries of great interest: Iraq, Iran, North Korea, and Libya. The article also answers some basic questions about nuclear programs, and recommends web-based resources for studying the problem of proliferation.