Biographies of film people and lists of their credits are obviously related. But frequently biographies and lists of film credits also contain movie plot summaries, and in some resources the plot synopsis is the main content. Consequently there's considerable overlap among these resources.
Biographies give an interpretation of a person's work and its background. They range from popular "life stories" to sophisticated critical analyses. Autobiographies naturally present a person's own views, with the resulting benefits and biases. The short entries in biographical dictionaries and encyclopedias can only hit the highlights, so if you want fuller information and analysis, search for the person as a subject in Orbis. Directors, actors, producers, screenwriters, even cinematographers may have biographies or autobiographies.
Movie credits usually strive to be exhaustive, but don't offer background. They are useful for tracing the outline of a person's work. For production crew, credits may be the only information available. Some of the resources below give credits back to 1895.
Plot summaries may stick strictly to the facts of the storyline, or incorporate discussions of the theme, tone or other aspects of the film.
See also the resources listed under Dictionaries & Encyclopedias (many give short bios and plot synopses) and Guides & Companions (serve as a kind of introduction to some group of films and filmmakers).