Photocopying an entire book is a violation of copyright. You may photocopy a few pages or small section. A good rule of thumb is to limit photocopying to a very small portion of the entire text.
Fair Use is a limitation that allows reproduction of copyrighted materials under certain circumstances, without securing the copyright owner's permission. Fair Use acknowledges the importance of the educational use of copyrighted works, by allowing reproduction for purposes such as comment, criticism, news reporting, teaching, scholarship, and research. Fair Use is comprised of the following four factors:
Materials that meet the four factors of fair use may be used without obtaining copyright permission. The four factors must be examined on an individual basis to determine whether copying represents fair use. The United States courts have maintained that no single factor is determinative.