While most online textbooks cost money, there are some sites that allow students to gain access to free online textbooks, according to Campus Technology. These sites typically earn money by selling advertising and offer source materials from other online resources and present them in digital book form.
Many conventional online book sellers allow students to purchase or rent digital copies of textbooks for a fee, according to Investopedia. These books are often digital copies of books that are published in print. The ability for students to access and use free books depends on the specific book a teacher requires for a class.