In the humanities, a primary source is a document that was created during the time period being studied. This includes newspaper and magazine articles, original film reviews, pamphlets, interviews, government publications, manuscripts, diaries, newsreels, and other sources that speak to the context of the time period. Primary sources provide firsthand evidence of historical events recorded by those who lived it, and as such usually need to be contextualized with more modern secondary sources like histories of the time period and academic film writing.

You can usually find clues to specific primary sources by looking through secondary materials like books and scholarly articles written in the present day. These often include bibliographies of the primary works used as references, and can give you ideas about other ways to search for your topic. Some more recent books also include reprints of primary sources.

Bowdoin College has an excellent guide for Reading/Evaluating Primary Sources — the PAPER acronym is a helpful way to think of what you should be doing with these documents.

In addition, the NYU Library has a somewhat broader overview, which also has links to other helpful sites (among them, ones dealing with primary sources we find on the web).

Lantern is an online archive for primary sources from various collections including the Hollywood System, Early & Global cinema, Fan Magazines, Technical journals, etc.