BookCrossing is a social activity that encourages reading and sharing books by registering books online and releasing them into public places to be found and read by others. Participants, called BookCrossers, track the journeys of books online as they are passed between readers. While libraries aim to lend books for a set time, BookCrossing treats books as gifts to spread reading. Some advantages are promoting reading habits and authors, though effectiveness is hard to measure as books can get lost. BookCrossing may provide insights into new ways of combining literature and the internet.