The concept of BookCrossing is similar to a message in the bottle. Books are given away or ‘released in the wild’ in the hope that future readers will leave a message to the original owner.
To participate, you register the book you intend to ‘release’ on the website where it is given an individual BCID number. You then label your book with a short explanation, the BookCrossing URL and the BCID (There are readymade templates on the site). Once that is done, you are ready to release your book, ie. place it somewhere that it will be easily found (like in a coffee shop, or a train station). The label requests anyone finding the book to log on to BookCrossing, leave a journal entry, and then to Read and Release the book again.
I am planning to release two books tomorrow.