Copyright protects “original works of authorship” that are fixed in a tangible form of expression. Copyrightable works include the following categories:

• Literary works
• Musical works, including any accompanying words
• Dramatic works, including any accompanying music
• Pantomimes and choreographic works
• Pictorial, graphic, and sculptural works
• Motion pictures and other audiovisual works
• Sound recordings
• Architectural works
• Computer programs

It is best to assume that anything published after 1928 is protected by copyright, even if it does not contain a copyright notice. The Library of Congress Copyright Office Circular 22 explains how to determine the copyright status of a work, when you are in doubt. A helpful summary of this publication can be found at the Copyright Information Center of the Cornell University Library.  Stanford University Libraries maintains a Copyright Renewal Database for books published in the U.S. between 1923 and 1963; if the copyright of a book published in this period was not renewed—and most were not—it is in the public domain.