It’s no surprise that writers spend a lot of time at the library. In line with Borges, but without his systematism, I argue that libraries can be understood as worlds in their own right, as the sum of all possible worlds. Writing in a library is like straddling a frontier. Behind you is the known, familiar, accessible world; in front, the unknown. This is where the Library of Babel lies, between what exists now and what is possible –between the superimposition of real libraries and the incommensurable possibilities offered by the book in progress, which, once completed, will join its comrades, taking up its place on the other side of the frontier.