An EPUB file is a widely-used format for digital publications, specifically designed for reflowable text content that adapts to different screen sizes. Unlike static formats like PDF, EPUB files dynamically adjust text size, line breaks, and images based on the reader's device, enhancing readability on smartphones, tablets, or dedicated e-readers. This reflowable nature relies on open web standards like HTML and CSS for content structuring and styling.

The EPUB format is the primary standard for e-books sold online by major retailers. It is used for distributing novels, textbooks, manuals, and other text-heavy publications. Major platforms like Apple Books, Google Play Books, Kobo, Adobe Digital Editions, and virtually all dedicated e-readers (excluding Amazon Kindle, which primarily uses its own AZW format) natively support EPUB files for reading.

EPUB offers significant advantages like device adaptability, accessibility features for readers with disabilities, and wide compatibility. However, it handles complex fixed layouts (like intricate comics or illustrated children's books) less effectively than formats like PDF or Amazon's fixed-layout KF8. Future EPUB versions continue to improve support for interactivity and richer multimedia while maintaining its core focus on text reflow. This evolution ensures it remains the dominant open standard for the global e-book industry.