We put you in the stocks and let people slap you with scholarly journals.
Just kidding! You will be charged a fine for every day it is late. Fines are typically 10 cents a day per item, but non-circulating items and items on reserve may be $1 a day or 15 cents per hour. Failure to pay will prevent you from being able to register for classes or obtain a transcript. But, you can also renew your books (typically up to 5 times) to avoid late fees.