You may have seen them in various locations around town—decorative boxes filled with books, free for anyone to take home and enjoy, inviting us all to come back and share a book another person might love. Book sharing boxes have been around for years (a social innovation widely credited to the late Todd Bol). They promote literacy, inspire a sense of community, and help cultivate new friendships among like-minded neighbors. Here's how to join in on the literary fun.