This document provides an introduction to child themes in WordPress. It defines a child theme as a theme that inherits functionality from a parent theme and allows modifications or additions to be made. Some advantages of child themes are that they allow for unique designs, an updatable parent theme, security, specialization, and temporary changes. Potential disadvantages are a steep learning curve, performance issues, and extra maintenance work. The document recommends considering child themes if your skills are advanced and the desired modifications are extensive. It outlines the directory structure for child themes and notes that the key files are style.css, functions.php, and template files.