The Progressive League was a British organisation for social reform and the promotion of scientific humanism, founded in 1932 by H. G. Wells and C. E. M. Joad under the name "Federation of Progressive Societies and Individuals" (FPSI).

One of the first of a generation of non-governmental organisations, as influenced by Wells' idea of the "open conspiracy", the organisation had its heyday in the 1930s and 1940s, advancing liberal and humanistic approaches to many of the issues that animated the concerns of contemporary intellectuals and freethinkers. The organisation became quieter in the later part of the 20th century as numerous other organisations sprang up as specialised advocates for many of the same causes – many of which had originally spun-off from the League, such as the Marriage Law Reform Society. At the same time, within the humanist movement, other organisations such as the British Humanist Association became prominent as broad platform campaigners for social reform.

In 1931 J. B. (Jack) Coates wrote to the Rationalist Press Association's (RPA) Literary Guide, advocating a form of scientific humanism, which he associated with Bertrand Russell, H. G. Wells and Julian Huxley:

The great work of the modern period, these eminent thinkers argue, is the framing of constructive moral and social policies. The special work of the modern Rationalists should be, therefore, to direct the modern world conscience so as to bring about that scientific world reconstruction which is the goal of the hopes of the scientific humanist.

His call produced a large response in subsequent issues of the Literary Guide. He was opposed by many, however, including the leading rationalist J. M. Robertson, but gained support from the veteran rationalists F. J. Gould, Archibald Robertson and especially C. E. M. Joad, who wanted Conway Hall to become the headquarters of "an association of progressive organizations with humanist aims."

In what became known within the movement as the "Great Conway Hall Plot", a group of nine RPA "modernisers", including Joad, Robertson, Coates and John A. Hobson, stood for the RPA Board on a "scientific humanism" platform. The plot failed and Robertson resigned from the Board in March 1932.

In early 1932 the Conway Hall plotters met at Joad's house, where they decided to form an independent group, the Federation of Progressive Societies and Individuals. The Federation's first conference took place in France, at a chateau owned by Pryns Hopkins. Individual members were invited to a meeting in April 1932.

Meanwhile, on 20 August 1932 the New Statesman published a call from H. G. Wells for a Federation of X Societies, "open conspirators to change the world." It was suggested to Joad that he contact Wells, and on 11 September 1932 another conference took place, this time in England.