Les XX (Les Vingt) was a group of twenty Belgian painters, designers and sculptors, formed in 1883 by the Brussels lawyer, publisher and entrepreneur Octaaf Maus. For ten years they held an annual exhibition of their art and 20 other international artists were invited to participate in their exhibition. such as Camille Pissarro, Claude Monet, Lautrec, Crane, Georges Seurat, Paul Gauguin and Paul Cézanne. There were a total of 126 guests at the ten editions. From the Netherlands they were George Breitner, Thorn Prikker, Floris Verster, Isaac Israels and Vincent van Gogh.

Without a clearly defined program, but united by aversion to academicism and a drive for innovation, the Vvingtists sought close ties with (neo-)impressionism, symbolism and Art Nouveau. Les XX was in a sense a successor to another group, L'Essor. The rejection of Ensor's The Oyster Eater in 1883 by L'Essor Salon, following the earlier rejection by the Antwerp Salon, was one of the events that led to the formation of Les XX.

Maus maakte met Edmond Picard en de Belgische dichter Emile Verhaeren ook het bijbehorende tijdschrift L'Art Moderne , dat  al in 1881 van start ging. Deze publicatie verdedigde Les XX met scherpe polemieken tegen aanvallen van critici. 

The exhibitions of 1884, 1885 and 1886 were held in the Center for Fine Arts. The later exhibitions were all held at the Museum of Modern Art of Brussels. In 1894 it was decided by majority vote to dissolve the group and was succeeded by La Libre Esthétique (1894-1914 with Maus and Van Rysselberghe as initiators. The emphasis here was mainly on the decorative arts, with which the Art Nouveau of mainland Europe began with including Architects Horta and Van de Velde. Les Vingt was an important model for many groups that followed, such as the Wiener Sezession.