Grass: A Nation's Battle for Life is a 1925 documentary film that follows a branch of the Bakhtiari tribe of Lurs in Persia as they and their herds make their seasonal journey to better pastures. It is considered one of the earliest ethnographic documentary films. In 1997, Grass was selected for preservation in the United States National Film Registry by the Library of Congress as being "culturally, historically, or aesthetically significant."

A documentary film or documentary is a non-fictional motion picture intended to "document reality, primarily for instruction, education or maintaining a historical record". Bill Nichols has characterized the documentary in terms of "a filmmaking practice, a cinematic tradition, and mode of audience reception [that remains] a practice without clear boundaries".