Les XX was a group of twenty Belgian painters, designers and sculptors, formed in 1883 by the Brussels lawyer, publisher, and entrepreneur Octave Maus. For ten years 'Les Vingt' (pronounced French pronunciation: [lɛ vɛ̃]), as they called themselves, held an annual exhibition of their art; each year twenty international artists were also invited to participate in the exhibition. Artists invited over the years included: Camille Pissarro (1887, 1889, 1891), Claude Monet (1886, 1889),Georges Seurat (1887, 1889, 1891, 1892), Paul Gauguin (1889, 1891), Paul Cézanne (1890), and Vincent van Gogh (1890, 1891).
It was founded on 28 October 1883 in Brussels and held annual shows there between 1884 and 1893, usually in January-March. No president or governing committee. The group was formed by 11 artists dissatisfied with the conservative policies of the organization L’Essor and the official academic Salon. L'Essor ('Soaring') was set up also in opposition to the Salon, but with a strong bureaucratic element of twenty Essorians comprising a governing committee. Octave Maus (lawyer, journalist, art critic) acted as the secretary of Les XX, which was free of stifling regulations. The extent of governing was done by a rotating committee of three which organized the exhibitions. In addition to the twenty members, twenty international invitees would also exhibit. During the exhibitions, there were also literary lectures and discussions, and performances of new classical music, organised from 1888 on by Vincent d'Indy, with from 1889 until the end in 1893 very frequent performances by the Quatuor Ysaÿe.
Octave Maus, Edmond Picard and Emile Verhaeren (Belgian poet) were the driving force of the associated review, L'Art Moderne, created in 1881. There was a close tie between art, music and literature among the Les XX artists.