The New Reasoner was a British journal of dissident Communism published from 1957 to 1959 by John Saville and E. P. Thompson.

The editors proposed the use of the journal as a forum for the discussion of "questions of fundamental principle, aim, and strategy," critiquing Stalinism as well as the dogmatic politics of the Communist Party of Great Britain (CPGB).

The Reasoner took its name from an early 19th-century publication which had attempted to renew and reinvigorate a flagging Jacobin Radicalism.

In 1957, following their resignation from the CPGB over its support of the Soviet Union's invasion of Hungary, Thompson and Saville began the publication of a new journal, named the New Reasoner, with the purpose of contributing to "the re-discovery of our traditions, the affirmation of socialist values, and the undogmatic perception of social reality."

The opening editorial was a reaffirmation of their commitment to the British Marxist and Communist tradition, despite their departure from the Party.