Nothing! It is a free book lending service but we have a limited number of books for lots of people so have to lend for a limited time only (3 weeks or 1 week at a time). However, you can renew this loan up to 4 times without bringing it back before we need to see it. If you are late back, there is a small fine but we do send you a reminder to make sure you renew. If you can't do it online, you can ring us instead.