The International Marxist Group (IMG) was a Trotskyist political party in the United Kingdom between 1964 and 1987. The party published the newspaper Red Mole .

It emerged from a group of International Secretariat of the Fourth International (ISFI) loyalists, including Ken Coates within the Revolutionary Socialist League (RSL), who launched a magazine, The Week. They then split from the RSL to form the International Group. After the ISFI became the United Secretariat of the Fourth International (USFI), they ordered the RSL to unite with the International Group. This happened in 1964, but very soon the former International Group members split to form a new International Group, and in 1965 the USFI demoted the RSL to a "sympathising" group after which the RSL continued on the road to becoming well known as the Militant Tendency.

In 1968, the International Group renamed itself as the International Marxist Group, and became prominent when Tariq Ali led protests against the Vietnam War. The IMG began to focus on work in the student movement, expelling some members who formed the Revolutionary Communist League. During the 1970s, increasing division appeared in the group, but it remained fairly large and launched the Socialist Unity initiative for the 1979 general election. Between 1979 and the crisis of the mid 1980s the IMG organised a youth organisation called Revolution Youth - renaming itself Revolution and entering the Labour Party Young Socialists in 1981.

In 1982, the IMG renamed itself as the Socialist League. The group entered the Labour Party and began publishing the Socialist Action newspaper. When this group split in 1985, a minority, led by Phil Hearse, Dave Packer, Davy Jones, and Bob Pennington formed the International Group, which in 1987 merged with the Socialist Group to form the International Socialist Group and publish Socialist Outlook.

The remaining majority of the of the Socialist League, consisted of two factions. One, the pro Socialist Workers Party (US) faction, was led by Brian Grogan. The majority faction was led by John Ross. The Grogan group soon also split away, leaving the Ross group as Socialist Action.