Documentaries are significant in their ability to reveal new realities not typically seen in fiction films and to challenge our experiences and ideas. They may also present a well-known subject in a new light, or confront viewers’ assumptions about a particular position, person, or issue.

The two primary traditions of documentary are the social documentary and ethnographic film.

Social documentaries examine and present both familiar and unfamiliar peoples and cultures from around the world from a perspective that focuses on a particular problem or social issue. A form of social documentary, political documentaries aim to investigate and to criticize or celebrate the political activities of men and women within the social sphere. Political documentaries that explicitly support specific social or political issues are sometimes considered propaganda films. Another subset of the social documentary, the historical documentary is a type of film that concentrates largely on recovering and representing events or figures in history.

Ethnographic documentaries are cultural explorations aimed at presenting specific peoples, rituals, or communities that may have been marginalized by or are invisible to the mainstream culture. Two practices within this tradition include anthropological films and cinéma vérité. Anthropological films explore different global cultures and peoples, both living and extinct. The French documentary movement of cinéma vérité presents real objects, people, and events in a confrontational way, with the subject acknowledging the reality of the camera recording it. The North American version of cinéma vérité, referred to as direct cinema, is more observational and less confrontational than the French practice.

In recent years some new types of documentaries have emerged that blur the boundaries between social documentaries and ethnographic films and even between nonfiction and fiction. Personal or subjective documentaries create films that look more like autobiographies or diaries. Reenactments use documentary techniques in order to re-create presumably true or real events. Mockumentaries take a much more humorous approach to the question of truth and fact by using a documentary style and structure to present and stage fictional subjects.