“Why doesn’t my instructor want me to use Wikipedia as a source?” Wikis are sites that users can add to and edit as they see fit; as a result, their contents are not always reliable. It’s true that Wikipedia, a hugely popular site, has such a large and enthusiastic audience that users are likely to catch mistakes and remove deliberately false information quickly. But you can never be certain that a wiki entry has not been tampered with. Use wikis as sources for preliminary research and then make sure that you double-check any information you find there.