Sidney James Webb, 1st Baron Passfield (13 July 1859 – 13 October 1947) was a British socialist, economist, reformer and a co-founder of the London School of Economics. He was one of the early members of the Fabian Society in 1884, along with George Bernard Shaw (they joined three months after its inception). Along with his wife, Beatrice Webb, Annie Besant, Graham Wallas, Edward R. Pease, Hubert Bland, and Sydney Olivier, Shaw and Webb turned the Fabian Society into the pre-eminent political-intellectual society of England in the Edwardian era and beyond. He wrote the original Clause IV for the British Labour Party.
Webb was born in London to a professional family. He studied law at the Birkbeck Literary and Scientific Institution for a degree of the University of London in his spare time, while holding down an office job. He also studied at King's College London, prior to being called to the Bar in 1885.
In 1892, Webb married Beatrice Potter, who shared his interests and beliefs. The money she brought with her enabled him to give up his clerical job and concentrate on his other activities. In 1895 he helped to establish the London School of Economics, using a bequest left to the Fabian Society. He was appointed its Professor of Public Administration in 1912, a post which he held for fifteen years.