The Social Democratic Federation (SDF) was established as Britain's first organised socialist political party by H. M. Hyndman, and had its first meeting on 7 June 1881. Those joining the SDF included William Morris, George Lansbury, James Connolly and Eleanor Marx. However, Friedrich Engels, Karl Marx's long-term collaborator, refused to support Hyndman's venture. Many of its early leading members had previously been active in the Manhood Suffrage League.

Henry Mayers Hyndman was an English writer, politician and socialist.