Théophile "Théo" van Rysselberghe (; French: [teofil teɔ vɑ̃ ʁisɛlbɛʁɡ]; 23 November 1862 – 13 December 1926) was a Belgian Neo-Impressionist painter who played a pivotal role in the European art scene at the turn of the twentieth century. A founding member of the Belgian avant-garde group Les XX, he was an important figure in the international Neo-Impressionist movement and helped connect the artistic circles of Brussels and Paris with wider European cultural networks. His work was distinguished by its innovative treatment of colour and light, particularly in his portraits and landscapes.
Born in Ghent and trained at the Academy of Ghent and the Académie Royale des Beaux-Arts in Brussels, van Rysselberghe initially worked in a realist and Orientalist style. His extensive travels in Spain and Morocco during the 1880s strongly influenced his interest in light and colour. After encountering Impressionism and, in 1886, Georges Seurat's A Sunday Afternoon on the Island of La Grande Jatte, he adopted Neo-Impressionism and became one of its leading practitioners outside France.
Through Les XX and later La Libre Esthétique, van Rysselberghe played an important role in the international circulation of avant-garde art, helping bring the work of Seurat, Paul Signac and other French artists to Belgian and wider European audiences. His extensive artistic and literary connections included artists and writers such as Signac, James Ensor, Émile Verhaeren, Henry van de Velde and André Gide. Van Rysselberghe developed a distinctive and highly personal form of Pointillism, adapting the systematic principles of French Neo-Impressionism to his own expressive use of colour and light. His luminous portraits and landscapes transformed the technique into a distinctive decorative and expressive style, giving his work a character distinct from that of Seurat and other French Neo-Impressionists.
From around 1900, van Rysselberghe gradually moved away from strict Pointillism, replacing its regular dots with broader and more fluid strokes while retaining his characteristic concern with colour and light. His later work extended beyond Neo-Impressionism into landscapes, seascapes, monumental nudes and decorative compositions, particularly after his move to the south of France.