Write down all the International Standard Book Number numbers for your books. You can usually find a book's ISBN number printed on the outside back cover.
Visit the BookByte, Money for Books, Textbook Buyer, Book Buyer Online, Books Into Cash and Barnes & Noble websites and enter the ISBN numbers in the form provided to get a quote. Try each websites to see which offers you the most for your textbooks. Some sites provide a prepaid shipping label if you accept the offer.
Pack the books into a box once you have settled on the company you will sell them to. Enclose any packing information the company has requested, attach the shipping label and mail it. The company will inspect the book's condition upon arrival and pay you for them upon approval.