Atlanticism is a philosophy of cooperation among Western European and North American nations (specifically the United States, and Canada) regarding political, economic, and defense issues, with the purpose to maintain the security of the participating countries, and to protect the values that unite them: "democracy, individual liberty and the rule of law." North Atlantic Council. blank">"Riga Summit Declaration," 2006-11-29. Retrieved on 2007-10-13 One who shares the idea of Atlanticism is known as an Atlantist or an Atlanticist; the name derives from the _Atlantic Ocean that separates the two continents — or, as sea-faring nations will say, the ocean that connects the two continents. Atlanticism is alien to continentalism.

The North Atlantic Council is the premier, governmental forum for discussion and decision-making in an Atlantic context. Well-known Atlanticists include former British Prime Minister Tony Blair, current British Prime Minister Gordon Brown, Zbigniew Brzezinski and Javier Solana. NATO is an Atlanticist organization, and the F-35 Joint Strike Fighter is an Atlanticist project. Leaders of Eastern European countries such as Poland and Romania profess a strong Atlanticist view - one does not have to live in Western Europe (or North America) to be an Atlanticist.

Atlanticism has undergone significant changes in the 21st century in light of Islamist terrorism and the Iraq war, the net effect being a renewed questioning of the idea itself and a new insight that the security of the respective countries may require alliance action outside the North Atlantic territory. After the September 11, 2001 attacks, NATO for the first time invoked Article 5, which states that any attack on a member state will be considered an attack against the entire group of members. Planes of NATO's multi-national AWACS unit patrolled the U.S. skies and European countries deployed personnel and equipment. In 2006, the North Atlantic Council declared that NATO's key priority was to contribute to the peace and stability in Afghanistan. By the end of 2006, the Atlantic organization had about 32,000 troops in Afghanistan (including 11,000 Americans under its command). However, the Iraq war caused fissures between certain Western European states and the US as well as Eastern European states such as Poland. Countries which supported the Iraq war, such as Spain and Italy, saw their generally pro-Iraq war governments lose in recent elections. Tony Blair, however, was re-elected, notwithstanding his relationship with President Bush, and support for the Iraq war. The implication of Romania and Poland in secret CIA-run prisons from 2003 to 2005 (both countries denied the existence of such prisons) hurt the Atlanticist idea. More recently, Germany, and, in May, 2007, France, saw the election of Atlanticist-leaning leaders, notwithstanding wide-spread, continuing opposition to the war in Iraq. On the other hand, rivalry between NATO and the European Union had by 2007 all but caused relations between the two organizations to break down.