BookCrossing (as well BC, BCing or BXing) is identified as "the practice of leaving a book in a public or open place to be picked up and read by others, who then do the same". The word is derived from bookcrossing.com, a free online book club which started and supported the practice and helps to "make the whole world a library".

The 'crossing' or exchanging of books possibly will take any of numerous forms, together with wild releasing books in public, direct swaps with other members of the websites, or "book rings" in which books go in a set arrange to participants who desire to read a definite book. The community aspect of BookCrossing.com has full-grown and expanded in ways that were not predictable at the outset. As well as forum discussions, mailing lists and yearly conventions throughout the world.