Originally Posted by Joykins
The library buys a special license for only so many books and lends them out for a loan period that can be customized. Once they're all lent, they start up a waiting list. Just like your regular library does. Adobe Digital Editions manages the licensing/DRM stuff for epubs and pdfs, and those books (license) can be "returned" early, opening it up for the 1st person on the wait list, etc.; otherwise the license "expires" on the due date and the library gets the rights back to lend it out again. It's very similar to borrowing a dtb from the real library, only when it's due, the library takes it back and you don't have to do anything about it, no overdue fines!