Antarctic Treaty, an international agreement signed December 1, 1959, designed to preserve the continent of Antarctica, along with all other land and water south of latitude 60° south, for peaceful purposes, particularly for scientific research. The treaty took effect upon full ratification by the governments of the signatory nations in June 1961, to remain in force indefinitely.

The treaty bans any military operations, use of nuclear weapons, or disposal of radioactive waste in Antarctica; encourages the free exchange of information from scientific research conducted there; and forbids nations from making any new territorial claims on the continent. It made no ruling on existing territorial claims. The treaty was later extended to protect marine life within the Antarctic ecosystem and to prohibit mining activity for a 50-year period beginning in 1991.

The treaty grew out of the International Geophysical Year (July 1, 1957-December 31, 1958). Participating nations declared a moratorium on political differences and worked together in Antarctica to study sunspot activity and its effects on the earth and its atmosphere. The studies led to important scientific discoveries, especially the discovery decades later of a hole in the ozone layer, the part of the atmosphere that protects all living things from harmful rays of the sun.

The Antarctic Treaty was originally signed by 12 countries that had maintained research stations on the continent during the International Geophysical Year: Argentina, Australia, Belgium, Chile, France, Japan, New Zealand, Norway, South Africa, the Union of Soviet Socialist Republics (USSR), the United Kingdom, and the United States. By 1996, 41 nations, representing more than 80 percent of the earth's population, had signed the treaty. Of these 41, 27 nations were full voting members of the treaty organization. Provisions of the treaty can be changed only by unanimous agreement of the voting members.