The Modes of Documentary
John Grierson, the Godfather of British documentary, coined the term documentary in the 1920s, and defined it as the “creative treatment of actuality”. This definition is still central to a modern discussion of film theory, and the most respected of all documentary theorists is American Bill Nichols, whose important books include Introduction to Documentary.
Nichols defines what he calls the six modes of documentary; all non-fiction films display one or more of these traits in their construction, as there is often overlapping between the different styles and conventions.
Here is a promotional interview with Nichols about the book.