 It probably goes without saying that plagiarism and copyright violation are not allowed on Wikipedia. You can't just copy from a book or website to build a Wikipedia article. But since Wikipedia is a collaborative project where one person's work builds on another's and the pieces of an article come from many different places, it's worth looking at Wikipedia's rules about plagiarism and copyright violation and the problems they can cause in a little more detail. If you're improving an article that others started, you may come across some of these types of plagiarism. First, unattributed plagiarism. This is when text is copied into Wikipedia from another source, but there's no indication of where it came from. Then, plagiarism of cited sources. If a footnote is added to show where information came from, but it still keeps the exact wording of the source, that's another common form of plagiarism. And then there's close paraphrasing. This is when an editor takes source material, whether they cite it or not, and they rewrite it somewhat, but the basic structure and meaning of the source text is still there. With close paraphrasing, there may be several small phrases that match between the two texts. It's even possible to change every single word in a sentence and still end up plagiarizing through a close paraphrase, if the meaning and structure of the source is kept. For this reason, it's not a good idea to write for Wikipedia by copying a source and then rewriting it bit by bit. Instead, you should put the information into your own words from scratch, or use a quotation. Copyright violation is a different but related issue on Wikipedia. Many cases of plagiarism are also copyright violations, but for example, if an editor adds the lyrics to a pop song into the article about that song, this may violate copyright even though it is not plagiarism. And if an article about a court case includes passages from the ruling without indicating it, this is plagiarism even if the copied text is in the public domain and not subject to copyright restrictions. None of this is allowed on Wikipedia. If you come across plagiarism in a Wikipedia article, what should you do? Remove it. You may want to replace the plagiarized content with your own words, or you may want to simply cut it out. But if you find some, please don't just leave it, especially if you're going to be building on the article yourself. Removing content that doesn't belong is actually a great way to improve Wikipedia. The Wikipedia community has a broad spectrum of methods for finding and removing plagiarism. The most important is just people reading articles and checking sources and noticing when the style of a passage just doesn't quite fit. There are also bots that automatically check recent content for copyright violations and many users keep a particularly close eye on student projects in their areas of interest. Since Wikipedia article histories are public, plagiarism can be traced back to the user who added it, even months or years later. So please take extra care that you aren't introducing plagiarism to Wikipedia. Happy editing!