September 1942 - A U.S. effort, code-named the Manhattan Project, is formed in the midst of World War II to unlock the mysteries of the atom in pursuit of nuclear weapons.
December 1942 - The first controlled nuclear chain reaction is achieved by Dr. Enrico Fermi, one of the eventual leaders of the Manhattan Project, at the University of Chicago.
July 1945 - The first atomic bomb is tested by the United States in the valley of Jornada del Muerto, at the Trinity Test Site in New Mexico.
August 1945 - The United States drops atomic bombs on Hiroshima and Nagasaki in Japan, killing 130,000 people; thousands more later die from the effects of radiation.
August 1946 - The Atomic Energy Act is signed by President Truman, creating the Atomic Energy Commission and placing the new nuclear energy industry under civilian control.
December 1953 - President Eisenhower gives his "Atoms for Peace" speech, calling for nuclear energy to be allocated for the "peaceful pursuits of mankind."
July 1955 - Arco, Idaho, is the first U.S. town to be powered by nuclear energy.
September 1957 - President Eisenhower signs the Price-Anderson Act, protecting the nuclear-power industry from financial liability in the event of a power-plant accident.
October 1957 - The International Atomic Energy Agency is created under the auspices of the United Nations. The three main pillars of the IAEA's work are nuclear safety and security, science and technology, and safeguards and verification.
December 1957 - The first large-scale U.S. nuclear power plant begins operation in Shippingport, Pennsylvania.
1970 - 20 nuclear reactors are in operation in the United States. (A nuclear reactor is an individual operating unit-many nuclear power plants have more than one reactor.)
1974 - The Energy Reorganization Act eliminates the Atomic Energy Commission, creating instead the Energy Research and Development Administration and the Nuclear Regulatory Commission. The new agencies are charged with regulating the nuclear industry.
October 1977 - The Energy Research and Development Administration is absorbed by the Department of Energy.
March 1979 - The Three Mile Island Nuclear Power Plant in Pennsylvania suffers a partial core meltdown, resulting in the worst nuclear accident in U.S. history.
1986 - An accident at Chernobyl in the Soviet Union results in 31 deaths, with delayed illnesses and deaths estimated in the hundreds of thousands.
1990 - An all-time high of 112 U.S. nuclear reactors is reached, although no new plants have been ordered since 1978.
January 1994 - The United States begins purchasing the former Soviet Union's "downblended" highly enriched uranium for use in U.S. nuclear reactors in an effort to keep the material off the nuclear black market.
1996 - The Watts Bar 1 nuclear reactor in Tennessee is the last reactor to come on line in the United States.
2000 - The Nuclear Regulatory Commission renews the first of 26 reactor licenses it has extended as of April 2004.
February 2002 - The Bush administration introduces Nuclear Power 2010, a program to identify new plant sites, develop more advanced technology, and streamline the regulatory process.
2003 - Three companies apply for Early Site Permits.
2005 - After 25 years with no new projects initiated, a nuclear revival is under way across the United States. Three companies have applied for permits under Nuclear Power 2010; plans are now in the pipeline to relicense 18 reactors nationwide.