The Reform Club is a private members' club, owned and controlled by its members, on the south side of Pall Mall in central London, England. As with all of London's original gentlemen's clubs, it had an all-male membership for decades, but it was one of the first all-male clubs to change its rules to include the admission of women on equal terms in 1981. Since its foundation in 1836, the Reform Club has been the traditional home for those committed to progressive political ideas, with its membership initially consisting of Radicals and Whigs. However, it is no longer associated with any particular political party, and it now serves a purely social function.

The Reform Club currently enjoys extensive reciprocity with similar clubs around the world. It attracts a significant number of foreign members, such as diplomats accredited to the Court of St James's. Of the current membership of around 2,700, some 500 are "overseas members", and over 400 are women.

The club was founded by Edward Ellice, Member of Parliament (MP) for Coventry and Whig Whip, whose riches came from the Hudson's Bay Company, but whose zeal was chiefly devoted to securing the passage of the Reform Act 1832. The club held its first meeting at No. 104 Pall Mall on 5 May 1836.

This new club, for members of both Houses of Parliament, was intended to be a forum for the radical ideas which the First Reform Bill represented: its purpose was to promote "the social intercourse of the reformer of the United Kingdom".

The Reform Club's building was designed by renowned architect Sir Charles Barry and contracted to builders Grissell & Peto. The new club was built on palatial lines, the design being based on the Palazzo Farnese in Rome, and its Saloon in particular is regarded as the finest of all London's clubs. It was officially opened on 1 March 1841. Facilities provided included a library which, following extensive donations from members, grew to contain over 85,000 books.

After the Second World War and with the old Liberal Party's further decline, the club increasingly drew its membership from civil servants. The club continued to attract a comprehensive list of guest speakers including Government Ministers Nick Clegg and Theresa May (2011), Archbishop John Sentamu (2012), and Ambassador Liu Xiaoming (2013).

Besides having had many distinguished members from the literary world, including William Makepeace Thackeray and Arnold Bennett, the Reform played a role in some significant events, such as the feud between Oscar Wilde's friend and literary executor Robbie Ross and Wilde's ex-lover Lord Alfred Douglas. In 1913, after discovering that Lord Alfred had taken lodgings in the same house as himself with a view to stealing his papers, Ross sought refuge at the club, from where he wrote to Edmund Gosse, saying that he felt obliged to return to his rooms "with firearms".

Harold Owen, the brother of Wilfred Owen, called on Siegfried Sassoon at the Reform after Wilfred's death. Sassoon wrote a poem entitled "Lines Written at the Reform Club", which was printed for members at Christmas 1920.