Reference sources provide summaries of topics by distilling primary and secondary sources for the general reader. For this reason they are excellent starting points for a research project because they can provide a lay of the land for someone new to a topic. Additionally, reference sources provide useful bibliographies curated by experts in the field. Dictionaries, encyclopedias, and handbooks are all useful reference sources.
Didn't find what you need in the specialized resources above? Then try simultaneously searching across multiple online reference works in the resources listed here.