This document provides guidance on writing effective alternative text (ALT-text) for images on webpages. It defines what ALT-text is, its functions for screen readers and browsers, and when and how to write ALT-text for different types of images, such as decorative, content, and functional images. The document also provides examples and explanations for writing correct and incorrect ALT-text through various scenarios to help the reader understand how to determine what information to include in ALT-text.