Socialist Action is a small socialist group in the United Kingdom. It was founded in 1981 when the International Marxist Group entered the Labour Party. Officially named the Socialist League, it became universally known by the name of its publication, Socialist Action.

Its character changed in a wave of splits in the late 1980s, beginning in 1985 producing the International Group, which merged with the Socialist Group and is now the International Socialist Group.

In 1998 a minority split to from the now defunct Communist League - the British co-thinkers of the Socialist Workers Party (USA).

The remainder of the group is now a small group that drew pessimistic conclusions from the fall of the Stalinist regimes in the Soviet Union and Eastern Europe. They continue to define themselves as a Trotskyist group but have have displayed an increasing tendency to ally with Stalinist formations and political positions. At the time of the split, the group was given equal status within the United Secretariat of the Fourth International with the International Group, but they are no longer affiliated.

Working with increasing secrecy in the Labour Party, they became supporters of Ken Livingstone and The Socialist Campaign Group of Labour MPs. They are involved in the publication of Socialist Campaign Group News and their members have mainatained leading poistions in many campaigns - the National Abortion Campaign , the Campaign for Nuclear Disarmament and various coalitions against the wars against Iraq, Afghanistan and Yugoslavia, for example. As a result, Socialist Action exert an influence beyond that which might be expected from so small a grouping.

In 2001 they stopped publishing their journal, also named Socialist Action, but continue to work together as a faction, for instance in the Student Broad Left and playing leading roles in organising the 2004 European Social Forum, and to publish occasional pamphlets and leaflets.