Encyclopedias can provide a great introduction to a topic. In general, relying heavily on encyclopedias as the basis of college-level work is frowned upon. Two good uses for encyclopedias: (1) get yourself up to speed on a topic and identify key issues and possible search terms; (2) use their Works Cited pages to get leads to actual primary and secondary literature on a topic. Those are the types of things you should be citing in your academic work.
Wikipedia can be a great first stop to bring yourself up to speed on a topic. Stephen Colbert demonstrates why it may not be the best choice to cite as a scholarly source.