The Solidarity Federation (SF; SolFed) is a British anarcho-syndicalist political organisation. It advocates for the abolition of capitalism and the state through industrial action, which it agitates for in industrial networks and local groups.

Originally established as the Syndicalist Workers Federation (SWF) in 1950, it became the British section of the International Workers' Association (IWA). In 1979, it reorganised into the Direct Action Movement (DAM), which participated in a number of industrial disputes during the 1980s and organised a short-lived couriers' union. Splits of anarchist communists from the organisation preceded its reorganisation into the Solidarity Federation, which it took the form of in 1994.

During the Spanish Civil War, many British anarchists moved towards anarcho-syndicalism and formed syndicalist organisations to support the Spanish National Confederation of Labour (CNT). After the defeat of the Spanish anarchists in the war, the British anarchist movement attempted to reorganise itself, culminating in the establishment of the Anarchist Federation of Britain (AFB), which included anarchists of various different tendencies.

By the end of World War II, syndicalists had risen to the leadership of the AFB, causing a split in the organisation. In August 1950, the syndicalists that were left over in the AFB reorganised into the Syndicalist Workers Federation (SWF). The SWF affiliated itself to the International Workers' Association (IWA), a syndicalist political international, as the organisation's British section. The SWF was broadly syndicalist in orientation, rather than specifically anarcho-syndicalist. Many of the initial members of the SWF were pacifists, who rejected violence as a means of class conflict.

The SWF experienced a period of growth through the 1950s and 1960s. In 1965, an estimated 150 syndicalists were organising in Britain; 100 were affiliated with the exiled CNT and 50 with the SWF. During the late 1970s, the structures of the SWF began to change under the influence of new members, who had filtered into the organisation from the punk subculture. By the end of the decade, it only had one remaining local branch, located in Manchester.

In March 1979, the remaining members of the SWF reorganised themselves into the Direct Action Movement (DAM), which experienced a period of growth throughout the early 1980s. The DAM initially sought support from the international syndicalist movement, but its organisational capacity was weak and British trade unionism was comparatively strong, so it was only capable of supporting existing industrial unions in Britain. Although the successor to an older organisation, the DAM themselves acknowledged that "syndicalism in this country has not really existed since the early 1920s." Its Direct Action magazine, initially edited in the cut-and-paste style of a punk fanzine, took a more serious and professional editorial style when reporting on the industrial disputes of the 1980s.

The DAM supported the miners' strike of 1984–1985, which it recognised as a movement directed by the union rank-and-file, in spite of its own criticisms of the authoritarian politics of NUM leader Arthur Scargill. The DAM raised funds for miners' support groups, protested on picket lines and organised a congress to encourage solidarity actions from workers in other industrial sectors. One member of the DAM, the Doncaster-based Dave Douglass, was one of the few striking miners that self-identified as an anarchist; he was also critical of the NUM leadership and organised direct actions to "improve the effectiveness of the miners' strike". In 1985, the DAM co-founded Anti-Fascist Action, within which it was active into the 1990s. The DAM later participated in the opposition to the poll tax and the protests against it.

In the late 1980s, the DAM began attempting to establish its own anarcho-syndicalist unions as an alternative to the reformist unions. Its only success on this front was the establishment of the Dispatch Industry Workers Union (DIWU), which organised delivery couriers from 1989 to 1992. This change in policy provoked a number of splits from the organisation, as some members thought all unions were inherently reformist, even if they were anarcho-syndicalist in orientation. In 1986, the group Syndicalist Fight (SyF) split off and later merged into the Anarchist Communist Federation (ACF); and in 1987, the Anarchist Workers Group (AWG) split off and later merged into the Revolutionary Communist Party (RCP).