William James Glackens (b. March 13, 1870, Philadelphia, Pennsylvania – d. May 22, 1938, Westport, Connecticut) was a U.S. realist painter.
Glackens studied at the Pennsylvania Academy of the Fine Arts and later moved to New York City, where he co-founded what came to be called the Ashcan School art movement. He was known for his dark-hued paintings of street scenes and daily life in the city's neighborhoods. One of the country's first realist painters, Glackens belonged to a group of artists dubbed by the press "the Eight Independent Painters" or The Eight, who chose to exhibit their works without pre-approval by the juries of the existing art establishment. The Eight exhibited at the Macbeth Gallery in New York City in 1908, showing works outside the controlling group's rigid definition of artistic beauty. The show went on to tour museums in nine U.S. cities over the next year. Other members of The Eight included Robert Henri and Maurice Prendergast.
During much of his career as a painter, Glackens also worked as an illustrator for newspapers and magazines in Philadelphia and New York City.
His brother was the cartoonist and illustrator Louis Glackens.