Fair use is a copyright principle that allows limited use of copyrighted works for commentary and criticism without permission. Copyright infringement can result in injunctions, damages and profits paid to the copyright holder, and even criminal penalties. When determining fair use, a judge considers the purpose and amount of the work used, its nature, and the effect on its potential market. For classroom use, teachers can use small portions of copyrighted works for instruction under fair use, but should get permission if using movies, music or large portions and consider purchasing materials when possible. To get permission, identify the owner and rights needed, negotiate payment and term of use, and plan ahead.