Libraries, like individuals, have rights under 17 U.S.C. Section 107 to make fair uses of copyrighted works. Most commonly they exercise these rights in one or another form with course reserves. Complying with fair use is not a simple task because fair use can be hard to understand. For example, Section 107 explicitly cites the practice of making multiple copies for classroom use as an example of fair use, but still requires the user to consider the "four factors" stated in the statute before deciding whether a particular use is fair:
The purpose and character of the use, including whether such use is of a commercial nature or is for nonprofit educational purposes;
The nature of the copyrighted work;
The amount and substantiality of the portion used in relation to the copyrighted work as a whole; and
The effect of the use upon the potential market for or value of the copyrighted work
For more information on fair use, please see the fair use portion of the Copyright Crash Course.