Grass: History of Marijuana is a 1999 Canadian documentary film directed by Ron Mann, premiered at the Toronto International Film Festival, about the history of the United States government's war on marijuana in the 20th century.

[1] The film follows the history of US federal policies and social attitudes towards marijuana, beginning at the turn of the twentieth century.

The film places much of the blame for marijuana criminalization on Harry Anslinger (the first American drug czar) who promoted false information about marijuana to the American public as a means towards abolition.

The film ends during the Bill Clinton administration, which had accelerated spending even further on the War on Drugs.

The film was generally well received by critics, scoring 64 out of 100 in Metacritic,[5] and a rating of 75% on Rotten Tomatoes.