Fair use allows limited use of copyrighted works without permission for purposes such as commentary, news reporting, and teaching. To determine fair use, one considers the amount and substantiality of the portion used, the use's nature and purpose, and how it affects the work's commercial value. Copyright infringement occurs when someone exploits a copyrighted work's exclusive rights without permission. Works in the public domain are not owned or controlled by anyone and can be used freely, including works whose copyright has expired or were released into the public domain. Creative Commons licenses allow creators to specify some reserved rights for others to use their works, such as requiring attribution or prohibiting commercial use.