Students know from experience how valuable Wikipedia can be when looking for quick background information about almost any topic. However, professors and librarians often say that Wikipedia articles should not be cited in papers. One reason for this has to do with the function of reference works. Encyclopedias typically provide only basic background information and not in-depth analysis. Other professors may disagree and say that some encyclopedia articles may be cited. Reference works vary greatly in nature, with some having more detail, context, and analysis than others. For example, the Smithsonian’s multi-volume Handbook of the North American Indian (print) and the Stanford Encyclopedia of Philosophy (online) are works of scholarship. If you get more than basic information from an encyclopedia or other reference work, you should consider citing it.
Perhaps the best advice is that Wikipedia can be useful as a starting point for many topics, especially obscure ones or those with a niche interest. Some articles are rich in detail, context, analysis, references, and suggestions for further reading. A rough rule of thumb, perhaps, is to be wary of articles on controversial or popular topics such as the Holocaust, but more trusting of articles on people, events, artistic works, social movements, etc., that you may not find in-depth anywhere else. A good example of a richly detailed Wikipedia article that engages the scholarly conversation is the one on the “American Frontier.” In some cases, Wikipedia articles will be as rich in detail and analysis as specialized works.
Wikipedia is a bit like "The Wild West" of scholarship. So, let the buyer beware!
(The text and ideas in this section come from Will Katerberg, Professor of History and Curator of Heritage Hall at Calvin University).