An online book is defined as a complete book that is made available through the Internet. Online books are different to regular ebooks because they are available directly on Internet pages, as opposed to a download, for example a PDF file download or an outdated EXE format ebook. Ebooks are also sometimes distributed on a CD or DVD, usually to increase the perceived value of a product without adding much cost to the actual production value of the product itself. This offline distribution method was more common before the Internet became more prevalent.

Several large websites have appeared in the last few years which give people access to thousands of these books. Some of the largest archives include Allosia Online Books, Project Gutenberg, The Sacred Text Archive, and the project of the University of Pennsylvania.

Project Gutenberg describes itself as the first and largest collection, however new projects including Allosia Online Books comes close to 250,000 texts, all available online. In many cases, companies including MSN help to digitize public text by sponsoring large digitization projects to make information available for free to everyone. This is generally done with content that exists in the public domain, including books which have expired copyright permission.

Many people like to sell ebooks as PDF files online, as the production cost is very low, meaning a higher profit margin - however this is always expected to be an extremely fast-moving market which companies like Clickbank help to moderate.

A major problem with online books is the inability to get them off the screen, so many people believe that they will never be able to truly compete with physical books. However technologies continue to emerge to change the paradigm - portable cheap and effective ebook readers can store thousands of ebooks at a time, and even more. Such digital devices can be taken with people anywhere, helping to retain the feeling of a physical book.