The Single Integrated Operational Plan (SIOP) was the United States' general plan for nuclear war from 1961 to 2003. The SIOP gave the President of the United States a range of targeting options, and described launch procedures and target sets against which nuclear weapons would be launched. The plan integrated the capabilities of the nuclear triad of strategic bombers, land-based intercontinental ballistic missiles (ICBM), and sea-based submarine-launched ballistic missiles (SLBM). The SIOP was a highly classified document, and was one of the most secret and sensitive issues in U.S. national security policy.

The first SIOP, titled SIOP-62, was finished on 14 December 1960 and implemented on 1 July 1961 (the start of fiscal year 1962). The SIOP was updated annually until February 2003, when it was replaced by Operations Plan (OPLAN) 8044. As of April 2013, the U.S. nuclear war plan was OPLAN 8010-12, Strategic Deterrence and Force Employment.

While much of the United States' nuclear war planning process remains classified, some information on the former SIOP planning process has been made public. The planning process began with the President issuing a presidential directive establishing the concepts, goal, and guidelines that provided guidance to the nuclear planners. The Secretary of Defense then used the President's guidance to produce the Nuclear Weapons Employment Policy (NUWEP) that specified basic planning assumptions, attack options, targeting objectives, types of targets, targeting constraints, and coordination with combatant commanders. The NUWEP was then used by the Joint Chiefs of Staff (JCS) to create the "Joint Strategic Capabilities Plan (JSCP), Annex C (Nuclear)." This document established a more detailed and elaborate set of goals and conditions that included targeting and damage criteria for the use of nuclear weapons. The final stage in the planning process occurred when the Strategic Air Command (SAC) (from 1961 to 1992) or the United States Strategic Command (USSTRATCOM) (from 1992 to 2003) took the guidance from the JSCP and created the actual nuclear war plan that becomes the SIOP. Detailed planning was carried out by the Joint Strategic Target Planning Staff (JSTPS) co-located with SAC Headquarters in Omaha, Nebraska.

As part of SIOP planning, Strategic Air Command (SAC, later USSTRATCOM) developed a set of plans and a series of options based on a target set known as the National Target Base (NTB). The number of targets in the NTB varied over time, from 16,000 in 1985 to 12,500 at the end of the Cold War in 1991, to 2,500 by 2001. The SIOP was primarily directed against targets in the Soviet Union (later Russia) but targets in the People's Republic of China, which had been part of the SIOP until the 1970s, were added back into the plan in 1997. In 1999, the NTB reportedly included targets in Russia, China, North Korea, Iran, Iraq, Syria, and Libya.

SIOP, and its renamed successors, is most importantly an "integrated" plan that uses both Air Force and Navy delivery systems; it is "single" only in the sense that it comes out of one planning group. The "plan" actually contains multiple "attack options" that are themselves complex plans.

There is no evidence that the Soviet Union's contingency plans from the end of World War II to 1950 were anything but routine and defensive, and the substantial postwar demobilization of the Soviet military supports the view that the USSR did not view a new war in Europe as likely. Although Soviet doctrine incorporated an assumption of innate hostility of the capitalist powers to Communism, Soviet leader Josef Stalin apparently believed that neither the USSR nor the West could afford to fight another world war, and was skeptical of the Western ability to raise an army large enough to occupy Soviet territory. Soviet planning thus emphasized defenses against nuclear bombing, and attacks on Western European bomber bases. Plans in 1946 and 1948 assumed that during war with an unspecified enemy, Soviet forces in Germany would assume defensive positions within the Soviet occupation zone and wait for reinforcements before counterattacking.

Soviet conventional forces greatly outnumbered the West's, however, and United States strategic nuclear strike plans were developed accordingly. While the United States was the only nation with the atomic bomb, in 1946 it had only 17 Silverplate B-29 bombers and 11 atomic bombs. Many early American war plans were based on using hundreds of nonexisting weapons; for example, an autumn 1945 plan envisioned using 196 atomic bombs on Soviet industrial targets, but SAC could not deliver such quantities until 1952. The bombs were of the Mark 3 type, weighing five tons and requiring 39 men two days to assemble. The press reported that "atomic-capable" B-29s were deployed to Britain in mid-1948 during the Berlin Blockade, by which time the US possessed about 50 atomic weapons. The Soviets likely knew through espionage, however, that none of the aircraft was a Silverplate; rather, they would have been used as part of plan DOUBLEQUICK, involving World War II-like sustained conventional bombing raids on Soviet air bases in Eastern Europe. Other than increasing its anti-aircraft defenses, the Soviets did not change its military preparations in any way during the blockade, unlike the reaction in the West. Although the Soviets launched an intensive public relations effort in 1949, aided by sympathetic Western European fellow travelers, to oppose the formation of NATO, the new alliance's military strength was so weak that the Politburo did not bother to discuss it for six months after its formation.

Strategic bombing during World War II of key transportation and energy sites was more effective than attacking cities, and early postwar non-nuclear war plans envisioned focusing on the Soviet petroleum industry. US war planners lacked updated maps of the USSR, however, and had to use pre-World War II maps—some older than the Russian Revolution—or perhaps German aerial photos from the war. Due in part to the lack of updated intelligence, nuclear planning increasingly focused on urban areas, which were easier to target and offered the potential for "bonus damage". The early Plan Totality targeted 20 cities with the 30 nuclear bombs then available. Plan BROILER (November 1947) envisioned 34 bombs on 24 Soviet cities. It and later plans such as HALFMOON (May 1948; 50 bombs on 20 cities) and OFFTACKLE (December 1949; 104 urban targets, 220 bombs, 72 more reserved for follow-up attacks) envisioned Western forces in Europe slowly retreating while the United Kingdom was reinforced as an air base for atomic attacks on the Soviet Union. President Harry S. Truman hoped for an international ban on atomic weapons and believed that the American people would not support their use for "aggressive purposes", and ordered JCS to devise a plan for conventional war; however, Secretary of Defense James Forrestal in July 1948 ordered it to stop and resume atomic war planning due to the Berlin crisis.