PRINT-only: There may be an e-book out there, although there often isn’t for older art/architecture/design monographs and exhibition catalogs. If a title is very important for independent work, a course, research paper, etc., feel free to e-mail me and I will investigate to see if an e-version is available for purchase. These can be purchased/turned “on” fairly quickly. There are many instances, however, where print is the only option, and while not ideal, I will do my best to help you identify alternatives.
Oxford Art Online and Oxford Bibliographies (Art History set of bibliographies, and other) are extremely useful resources for locating general information and bibliography about a topic. The latter, especially, does include mention of some online content as well as indications that a particular book is also available online.
