This guide will lead you to the best information resources related to museology.
Image source: Arad. GNU Free. The Metropolitan Museum of Art. Wikimedia Commons.
The amount of information available, as well as searching for and sifting through that information, can be overwhelming. Use this guide as you would a map; it'll help you find what you're looking for more efficiently.
A good place to start, particularly for background information, is Oxford Art Online.
Find auction catalogs, catalogues raisonnés, corpora, and museum catalogs under the Catalogs tab.
Need images? Under the Images tab, find links to image databases, information on how to search for embedded images, and websites that contain image collections.
Image Source: Map of Washington DC. Mrflip (Own work). Public domain. Wikimedia Commons.