Plagiarism on Wikipedia encompasses copy-and-paste plagiarism, close paraphrasing of another text, and unattributed quotations. Copyright violations are also heavily monitored and flagged.

Plagiarism and copyright violations are disruptive and time-consuming for volunteers to clean up. Except for brief quotations, copying content from copyrighted sources onto Wikipedia is against policy.

Wikipedia’s primary concern is with copyright violations, since it creates legal liability for the site. These violations most often take the form of image uploads to Wikipedia's sister site, Wikimedia Commons, which are then used to illustrate articles.