While Marie Kondo doesn't have any set rules as to how many books you should own, she personally keeps a 30-book collection. However, she doesn't necessarily expect you to do the same. In her book, The Life-Changing Magic of Tidying Up, she writes, "Keep only the books that will make you happy just to see them on the shelves, the ones that you really love.” Once you've followed her advice, you might be wondering what to do with all the books that you no long want.