For many years, the Bodleian Library curated a restricted collection of books that were considered to be too explicit for general access.
These books, many of which had sexual content, made up the “Phi” collection, bearing the Greek “Φ” on their spines like a mark of sin. Lloyd (Meadhbh) Houston (DPhil English, 2016) has published a history of the Phi Collection in the Bodleian Library Record (2015), which laid the groundwork for the current exhibition. You can read more about Lloyd’s research on Atlas Obscura, and if you are interested in visiting the free exhibition more details are available on the Bodeian website and in The Guardian.
Photo by Richard Ovenden, Bodley’s Librarian, via Twitter @richove