Bill Irwin (born April 11, 1950) is an American actor and clown noted for his contribution to the renaissance of American circus during the 1970s. He is known for his vaudeville-style stage acts, and has made a number of appearances on film and television.

Irwin was born William Mills Irwin in Santa Monica, California to Horace G. Irwin, an aerospace engineer, and Elizabeth (Mills), a teacher. He graduated from Oberlin College in 1973 with a degree in theater arts, and from the Ringling Brothers and Barnum & Bailey Clown College the following year. In 1975, he helped found the Pickle Family Circus in San Francisco, California. He left the company in 1979, and decided to pursue stage work.

Irwin created a run of highly regarded stage shows that incorporated elements of clowning, often in collaboration with composer Doug Skinner. These works included The Regard of Flight (1982), Largely New York (1989), Fool Moon (1993), The Harlequin Studies (2003), and Mr. Fox: A Rumination (2004). Mr. Fox is a production that Irwin has worked on for years, a biography of 19th century clown George Washington Lafayette Fox that also has autobiographical elements.

In 1996, Irwin performed with The Cadets Drum and Bugle Corps at the 1996 Summer Olympics, in a "band on the run" sequence where he played Dr. Hubert Peterson of the fictitious Federation of United Marching Associations of America.

Although Irwin is best known for his theatrical clown work, he has also been featured in a number of dramatic plays. Irwin appeared in 1988 on stage with Steve Martin and Robin Williams for a production of Waiting for Godot in the role of Lucky. Lucky's dialogue includes a famous 500-word-long monologue, an ironic element for Irwin since much of his clown-based stage work was silent. He appeared in 2002 with Sally Field in the replacement cast of The Goat or Who is Sylvia?. In 2005, he starred along side Kathleen Turner as George in a revival of Edward Albee's Who's Afraid of Virginia Woolf?.

Irwin's first featured film role was in 1980, in Robert Altman's Popeye starring Robin Williams. He has appeared in over 20 films, in brief supporting roles. Irwin's biggest film roles were in My Blue Heaven, a 1990 movie featuring Steve Martin and Rick Moranis, and Eight Men Out, which tells the real story of the Black Sox gambling scandal of 1919. He has also appeared in the film adaptations of How The Grinch Stole Christmas, The Laramie Project, and the 1999 film adaptation of A Midsummer Night's Dream.

His most notable television roles were Enrico Ballati, "The Flying Man", on the television series Northern Exposure, and Mr. Noodle in the Elmo's World segment of the PBS children's show Sesame Street. He has also appeared on The Cosby Show, Saturday Night Live, and 3rd Rock From The Sun. Irwin was featured in the 1988 music video of Don't Worry, Be Happy by Bobby McFerrin (along with McFerrin and Robin Williams).

In 2006 Irwin played the solitary character Mr. Leeds in M. Night Shyamalan's Lady in the Water.

Irwin was awarded the National Endowment for the Arts Choreographer's Fellowship in 1981 and 1983. In 1984 he was named a Guggenheim Fellow and awarded a 5-year MacArthur Fellowship. In 2005, he won the Tony Award for Best Actor in a Play for his appearance as George in the revival of Edward Albee's Who's Afraid of Virginia Woolf?.