First and foremost, there are tons of libraries here. Each college has its own then each faculty (subject) has its own. Then there's the Bodleian. The Bodleian is very old and houses many, many, many books - combined the Oxford libraries house 11 million books. Most are not on the open shelf meaning you must request them ahead of time and they are sent to the library of your choice. There are numerous manuscripts and old books you won't find anywhere else in the world. Furthermore, the Oxford Libraries receive, by law, a copy of every book published in the UK - this began in 1842. In short this means that the library system is rather complicated. I've yet to fully experience it as I won't be in the library system until Thursday. Nevertheless, I felt the libraries deserved a blog post.
You can see a map of all of the libraries, which shows you just how many there are, here.