As this classic, 1946 video explains, the U.S. government is divided into three parts: the Executive, Legislative, and Judicial branches. One of the first steps in using government documents and publications is deciding which federal agency deals with the information you need and figuring out under which of the branches that agency operates. A really thorough aid may be found at the Louisiana State University Library's Federal Agency Directory. This is most useful if you already know what department you're looking for, or if you want to locate under which branch a specific department or agency falls.