Reference sources and useful for finding the basic details of a topic: names, dates, places, related artists or themes, movements, etc. Consider these if you're struggling to define a topic, or as your next step after Wikipedia.
Scholarly art encyclopedia. Includes over 200,000 reference articles on every aspect of the visual arts from prehistory to the present, with selected images, written by over 6,800 scholars. Serves as the access point for Grove Art Online, the Benezit Dictionary of Artists, and other Oxford art reference resources. View a tutorial on this database here.