Tom Marioni (born 1937) is an American conceptual and performance artist based in San Francisco who has been a pivotal figure in West Coast conceptual art since the late 1960s. Born in Cincinnati, Ohio, he studied at the Cincinnati Art Academy before moving to San Francisco, where he became deeply involved in the city's experimental art scene.

In 1970, Marioni founded the Museum of Conceptual Art (MOCA) in San Francisco, one of the first artist-run spaces dedicated exclusively to conceptual and performance art. The museum, which operated until 1984, served as a vital gathering place and exhibition space for avant-garde artists including Vito Acconci, Dennis Oppenheim, Chris Burden, and Terry Fox, and helped establish San Francisco as an important center for experimental art.

Marioni's own artistic practice centers on the idea that art is primarily a social act. His ongoing work "The Act of Drinking Beer with Friends Is the Highest Form of Art" — begun in 1970 and regularly restaged — exemplifies his belief that the experience of communal gathering constitutes an art form in itself. His "Drum Brush Drawings," created by playing drums with wire brushes on paper, merge musical performance with visual art.

Marioni has also produced significant sculptural installations, sound works, and drawings throughout his career. He has exhibited internationally and received a Guggenheim Fellowship. His work is held by the San Francisco Museum of Modern Art, the Museum of Modern Art in New York, the Centre Pompidou, and the Smithsonian American Art Museum.