My husband Jack and I read books -- lots of books! When we're finished, we save them up and donate them to a local library. Then, they're either sold by library "friends" groups as part of fund-raising projects or, more common now since library funding has suffered substantial cuts, added to the regular collection available for lending. Since they tend to be popular titles, having extra copies helps keep library waiting lists a bit shorter (we hope). On the downside, I guess, our contributions likely will drop a bit since Christmas, when I got a Kindle e-book reader.