The group originated at the Revolutionary Tendency in the American Socialist Workers Party, formed in 1961, seeing themselves as loyal to the International Committee of the Fourth International while the SWP were keen to leave. After leaving the SWP and splitting, they renamed themselves in 1964, but were expelled from the ICFI in 1966.
The groups see themselves as a revolutionary propaganda group, and devote most of their time in attempts to polemicise with other socialist groups. This is often seen as simple disruption of these other group's activities. They undertake very little trade union activity. The International Bolshevik Tendency which split in 1985 claim that this has only been the case since they left the group. Another split occurred in 1996 when the League for the Fourth International left.
The US group publishes the newspaper Workers Vanguard and the theoretical journal Spartacist, while the UK group publishes Workers Hammer.