The Reagan Doctrine was a United States foreign policy strategy implemented by the administration of President Ronald Reagan to overwhelm the global influence of the Soviet Union in the late Cold War. As stated by Reagan in his State of the Union Address on February 6, 1985: "We must not break faith with those who are risking their lives—on every continent from Afghanistan to Nicaragua—to defy Soviet-supported aggression and secure rights which have been ours from birth." The doctrine was a centerpiece of U.S. foreign policy from the early 1980s until the end of the Cold War in 1991.

Under the Reagan Doctrine, the United States provided overt and covert aid to anti-communist guerrillas and resistance movements in an effort to "roll back" Soviet-backed pro-communist governments in Africa, Asia, and Latin America. The doctrine was designed to diminish Soviet influence in these regions as part of the administration's overall strategy to win the Cold War.

The Reagan Doctrine followed in the tradition of U.S. presidents developing foreign policy "doctrines", which were designed to reflect challenges facing international relations, and to propose foreign policy solutions. The practice began with the Monroe Doctrine in 1823, and continued with the Roosevelt Corollary, sometimes called the Roosevelt Doctrine, introduced by President Theodore Roosevelt in 1904.

The post–World War II tradition of presidential doctrines started with the Truman Doctrine in 1947, under which the U.S. provided support to the governments of Greece and Turkey as part of a Cold War strategy to keep both nations out of the Soviet sphere of influence. It was followed by the Eisenhower Doctrine, the Kennedy Doctrine, the Johnson Doctrine, the Nixon Doctrine, and the Carter Doctrine, all of which defined the foreign policy approaches of these respective U.S. presidents on some of the largest global challenges of their presidencies.

To watch the courageous Afghan freedom fighters battle modern arsenals with simple hand-held weapons is an inspiration to those who love freedom.

At least one component of the Reagan Doctrine technically pre-dated the administration. In Afghanistan, the Carter administration began providing limited covert military assistance to the Afghan mujahideen in an effort to drive the Soviets out of the country, or at least raise the military and political cost of the Soviet occupation of Afghanistan. The policy of aiding the mujahideen in their war against the Soviet occupation was originally proposed by Carter's National Security Advisor Zbigniew Brzezinski and was implemented by U.S. intelligence services. It enjoyed broad bipartisan political support.

Democratic congressman Charlie Wilson became obsessed with the Afghan cause, and was able to leverage his position on the House Appropriations committees to encourage other Democratic congressmen to vote for CIA Afghan war money, with the tacit approval of Speaker of the House Tip O'Neill, even as the Democratic Party lambasted Reagan for the CIA's secret war in Central America. It was a complex web of relationships described in George Crile III's book Charlie Wilson's War.

Wilson partnered with CIA officer Gust Avrakotos to create a small team that expanded U.S. support for the mujahideen, channeling aid through Pakistani president Zia-ul-Haq’s Inter-Services Intelligence (ISI). Avrakotos and Wilson charmed leaders from various anti-Soviet countries including Egypt, Saudi Arabia, Israel, and China to increase support for the rebels. Avrakotos hired Michael G. Vickers, a young paramilitary officer, to enhance the guerilla's odds by revamping the tactics, weapons, logistics, and training used by the mujahideen. Michael Pillsbury, a Pentagon official, and Vincent Cannistraro pushed the CIA to supply Stinger missiles to the rebels. Reagan's covert action program has been given credit for assisting in ending the Soviet occupation of Afghanistan.