William Moses Kunstler (July 7, 1919 – September 4, 1995) was an American lawyer and civil rights activist, known for defending the Chicago Seven. Kunstler was an active member of the National Lawyers Guild, a board member of the American Civil Liberties Union (ACLU) and the co-founder of the Center for Constitutional Rights (CCR), the "leading gathering place for radical lawyers in the country."

Kunstler's defense of the Chicago Seven from 1969 to 1970 led The New York Times to label him "the country's most controversial and, perhaps, its best-known lawyer". Kunstler is also well known for defending members of the Revolutionary Communist Party, Catonsville Nine, Black Panther Party, Weather Underground Organization, the Attica Prison rioters, Meir Kahane assassin El Sayyid Nosair, and the American Indian Movement. He also won a de facto segregation case regarding the District of Columbia's public schools and "disinterred, singlehandedly" the concept of federal criminal removal jurisdiction in the 1960s. Kunstler refused to defend right-wing groups, such as the Minutemen, on the grounds that "I only defend those whose goals I share. I'm not a lawyer for hire. I only defend those I love."

He was a polarizing figure; many on the right wished to see him disbarred, while many on the left admired him as a "symbol of a certain kind of radical lawyer." Even some other civil rights lawyers regarded Kunstler as a "publicity hound and a hit-and-run lawyer" who "brings cases on Page 1 and the NAACP Legal Defense Fund wins them on Page 68." Legal writer Sidney Zion quipped that Kunstler was "one of the few lawyers in town who knows how to talk to the press. His stories always check out and he's not afraid to talk to you, and he's got credibility—although you've got to ask sometimes, 'Bill, is it really true?'"