This document provides an introduction to the deep web, including its size, evolution, and how it can be accessed. The deep web refers to content that is not indexed by standard search engines and is much larger than the surface web that search engines can index. It includes dynamically generated pages that can only be accessed through a form and private pages that require login credentials. Sites on the deep web can only be accessed using special browsers and protocols like Tor that allow for anonymous surfing through onion addresses. While some deep web sites provide legal content, others are used for illegal activities and information sharing.