Until now, the best shelving systems on the market have largely addressed issues of versatility, load-bearing, assembly etc. When a generic shelf is used for storing books, it performs well either when completely full - not one book can be added or removed- or when it is supplemented with a number of bookends. Otherwise the books lose balance, fall to one side and eventually become damaged. We propose a shelf specifically thought for books; A bookshelf that takes advantage of the weight of the books to achieve a permanent state of equilibrium, regardless of the number of books sitting on the shelf: a living bookshelg. We have simply introduced a small inclination to what traditionally has been the horizontal shelf. The horizontal displacement of the modules allows for the creation of an infinite number of mosaic-like patterns on the wall, as well as accomodating books of different sizes. We presented a series of variations based on the same geometric principle of which the first, PEREC, was produced by PuntMobles (http://www.puntmobles.es/).