Art history is a vast discipline - geographically, historically, and intellectually. In its initial centuries, art history dealt with Western art, but the boundaries of the field have since (finally!) expanded. The canon continues to be redefined as histories of art in regions that had previously been ignored or marginalized are brought into the mainstream.
How to keep up with, or identify, all of the core literature of this field? Getting started with topical overviews and summaries written by art historians and experts through library encyclopedias or dictionaries is a great starting point, followed by looking at published bibliographies (comprehensive lists pointing you to published materials on a topic).
Online handbooks, dictionaries, encylopedias:
Print handbooks, dictionaries, encylopedias: