Gaitskellism was the ideology of a faction in the British Labour Party in the 1950s and early 1960s which opposed many of the economic policies of the trade unions, especially nationalisation and control of the economy.

Theoretically, it repudiated the long-standing orthodox position that identified socialism with public ownership of the means of production, and that such ownership was essential to achieve socialist objectives, and emphasized the goals of personal liberty, social welfare, and above all social equality. It downplayed loyalty to the labour movement as a central ethical goal, and argued that the new goals could be achieved if the government used appropriate fiscal and social policy measures within the context of a market-oriented mixed economy. Public ownership was not specifically rejected, but was seen as merely one of numerous useful devices.

The movement was led by Hugh Gaitskell and included Anthony Crosland, Roy Jenkins, Douglas Jay, Patrick Gordon Walker and James Callaghan, influenced by the teachings of London school economist Evan Durbin. Gaitskellites represented the political right of the Labour Party and were opposed by the Bevanites, the left-wing faction of the party led by Aneurin Bevan and Michael Foot. In the 1950s, there were many parallels between Gaitskellism and the economic policies of Rab Butler, the Conservative Chancellor of the Exchequer. This convergence of the two main parties was dubbed "Butskellism".

In the 1945 general election, the Labour Party won its first majority in Parliament, with Clement Attlee becoming prime minister. Both Gaitskell and Bevan took positions in the Cabinet, Gaitskell as Minister of Fuel and Power and Bevan as Minister of Health.

In October 1950, Stafford Cripps was forced to resign as Chancellor of the Exchequer due to failing health, and Gaitskell was appointed to succeed him. His time as Chancellor was dominated by the struggle to finance Britain's part in the Korean War which put enormous strain on public finances. The cost of the war meant that savings had to be found from other budgets. Gaitskell's budget of 1951 introduced charges for certain prescriptions on the National Health Service.

He had a falling out with Bevan, who had defended the NHS and had left over the matter, and the budget split the government. Harold Wilson and John Freeman joined Bevan in resigning in protest of Gaitskell's policies. Later that year, Labour lost power to the Conservatives in the 1951 election. Gaitskell was replaced as Chancellor by Rab Butler, who largely continued Gaitskell's economic policies. This was termed Butskellism and laid the foundation for the post-war consensus.

During the period of opposition, the feud between the Gaitskellites and Bevanites continued. In 1954, Gaitskell and Bevan ran against each other for the position of Treasurer of the Labour Party, which was seen as a stepping-stone to the position of Party Leader. Gaitskell defeated Bevan. Following Labour's defeat in the 1955 election, Attlee announced his retirement as Party Leader (and subsequently, Leader of the Opposition). In the leadership election, the Labour left rallied around Bevan, while the Labour right was split between Gaitskell and Herbert Morrison. Gaitskell defeated both, gaining almost sixty per cent of the vote, and on 14 December 1955 became both Leader of the Labour Party and Leader of the Opposition.

During the early period of Gaitskell's tenure as Party Leader, the opposition between the Gaitskellites and Bevanites simmered, centring mainly on the issues of nuclear disarmament (which the Bevanites supported and the Gaitskellites opposed) and Britain's participation in NATO, specifically the foreign policy of opposing the Soviet Union and supporting the United States (which the Bevanites opposed and Gaitskellites supported). However, during this initial period the factional infighting dimmed somewhat; Gaitskell appointed Bevan to the Shadow Cabinet as Shadow Colonial Secretary and then Shadow Foreign Minister, the position he held during the Suez Crisis which enabled him to formulate Labour's response to the actions of Prime Minister Anthony Eden. Also in 1956, Bevan was elected Party Treasurer, defeating the Gaitskellite candidate, George Brown. Ironically, in 1957 Bevan split from the Bevanites due to a speech he gave opposing nuclear disarmament at the annual Labour Party conference.