Reference works provide basic overview articles on various branches of knowledge. They may be general or subject-specific. They are excellent places to begin research on your topic. Reference works will provide general knowledge about your topic, help you develop a thesis, supply you with important keywords for searching, and provide you with citations to important primary and secondary works on the topic.
Some important reference works for the study of history are linked below. Many additional encyclopedias and dictionaries can be found in the Library Catalog, which you can access from the link to the bottom left.