This document provides an overview of EPUB ebooks, including what EPUB is, popular e-readers that support EPUB, features of EPUB 3, practical advice for creating EPUB ebooks, and resources for additional information. EPUB is an open standard for reflowable digital publications and documents, and defines a method for packaging web content like HTML, CSS, images and other files into a single file format for distribution. EPUB 3 adds support for multimedia, fixed layouts, scripting and digital rights management, though adoption of these features varies across readers. The document outlines workflows for authoring, validating and distributing EPUB ebooks.