The Taylor Institution serves as Oxford's center for the study of modern European languages and literatures. It has three libraries: the Main Library, the Modern Languages Faculty Library, and the Slavonic and Modern Greek Library. According to the Taylor Institution website, the research library "contains the largest specialist collection in this field in Britain." There are many rare books dating especially from the 17th century forward, though I myself visited to look at an early 16th century work in German. The reading room of the Main Library, located on the upper floor, is a beautiful place to work, with tall book shelves, paintings, and a fireplace.
