Bookcrossing.com is a website that allows users to print tracking labels for books, share books with strangers, and connect with other readers. These tracking labels allow the original user to track the journey of the book and to potentially start a dialogue with later readers of the same text.

This can be a useful tool for tracking the journey of a book, and can support activist efforts to share a specific message of idea.  One example of this, is an initiative to promote freedom of expression by sharing books that have frequently been challenged.