The Trades Union Congress is a voluntary association of trade unions which was formed in Manchester in 1868. It forms the largest pressure group in the United Kingdom and works to improve the rights and conditions of working people. In achieving its aims the TUC has played a role both in many Government organisations and in the political wing of the Labour movement. Such a history has resulted in its archives being a rich source for the study of the political, economic and social history of the United Kingdom in the twentieth century.

The TUC is governed by an annual Congress at which representatives of affiliated trade unions meet to determine policy and to elect the executive body of the organisation. Between 1869 and 1921, the executive work of the Congress was carried out by the Parliamentary Committee. In 1920, the Committee was composed of sixteen members who dealt with a relatively narrow range of labour affairs. Changes in society during the First World War led to a widening of the TUC's functions and consequently the formation of the General Council in 1921, which was composed of a representative sample of trade unionists. The General Council is assisted by a number of committees, including Finance and General Purposes, Disputes, Education, Organisation, Social Insurance, International, Economic and Production. These in turn are served by departments, the number and nature of which varies according to the needs and priorities of the time. The responsibility for the everyday work of the General Council lies with the General Secretary who is assisted by a Deputy General Secretary and one or two Assistant General Secretaries.

In the regions, the TUC is organised into Regional Councils which cover England and Wales. Trade union activity in Scotland and Northern Ireland is co-ordinated by the Scottish TUC and the Northern Ireland Committee of the Irish Congress of Trade Unions, both of which are separate organisations with close working relationships with the TUC. At a local level branches of affiliated trade unions unite to form trades councils.