Copyrighted materials can generally be used only by purchasing copies of the work or by obtaining permission from the copyright holder. However, the "fair use" exception allows limited use of copyrighted material without permission for educational purposes. Nevertheless, teachers need to be particularly careful about using copyrighted material in the classroom.
Public Domain Materials
Copyright law generally extends for several decades after the death of the author (after the death of the author, the copyright passes to the author's heirs unless sold to someone else). For this reason, materials that were published before January 1, 1923 (as well as certain other works) are almost always safe to use, because they have already passed into the public domain. This is why Shakespeare, for example, can be freely used in the classroom without copyright concerns. Copyrights do not attach to works produced by the U.S. federal government.
What Fair Use Is
Whether a particular use of a copyrighted work is fair or not is determined by courts on a case-by-case basis. For this reason, there are no "bright line" rules on fair use. Nevertheless, certain rules of thumb apply. For motion media, you may use 10 percent or a total or three minutes, whichever is less. For written materials, you may use the lesser of 1,000 words or 10 percent of the total. For music, lyrics and music videos, you may use up to 10 percent, but no more than 30 seconds of an audio recording.
If a copyrighted work is designed specifically for educational use (a textbook, for example), a teacher may not copy it for classroom use. Each student will have to buy his own copy. Copyright rules are stricter for educational materials than for other materials in order to protect the financial incentives that encourage people to produce educational materials in the first place.
The TEACH Act
U.S. copyright law was modified in 2002 with the enactment of the TEACH Act, which liberalizes the fair use exception with respect to copyrighted digital materials used in distance learning. Only accredited, non-profit educational institutions and certain government entities are eligible for TEACH Act protection.
Copyrighted materials generally have copyright notices attached (although this is no longer required by law). These notices usually provide contact details for the publisher. If you wish to obtain permission to use copyrighted material, you should contact the publisher with specifics that precisely identify the work you wish to use and explain the purpose of your intended use. Although you may or may not be charged a fee for your use, you will almost always be expected to provide proper attribution of the copyright owner (and perhaps the author as well, if the author no longer owns the copyright).