This is sort of like Netflix for books - you pay a monthly fee, make a list of books you'd like to read and they'll ship them to you usually in shipments of two books as quickly as you can read them. You can sign up for various levels, I have the 4 books at a time for $13. But I read two, ship them back get another two, etc., so I always have books coming and going and I figure they probably send me about 8 books a month so that works out to less than $2/book. It's only paperbacks, though, but they have a very large selection.