Leo Castelli (September 4, 1907 – August 21, 1999) was an Italian-American art dealer who originated the contemporary art gallery system. His gallery showcased contemporary art for five decades. Among the movements shown were Surrealism, abstract expressionism, Neo-Dada, pop art, op art, color field painting, hard-edge painting, lyrical abstraction, minimalism, conceptual art, and neo-expressionism.

In 1957, he opened the Leo Castelli Gallery in a townhouse in New York City. From the mid-1960's through the 1970's, the gallery was perhaps the most prominent commercial venue for art in the world. He gave Johns, Stella and Lichtenstein their first one-man shows.