This document provides an overview of plug-ins for the DITA-OT toolkit and how to develop plug-ins to customize or extend the toolkit's functionality. It discusses extension points that plug-ins can integrate with, how the integrator.xml file handles plug-ins, the required plugin.xml file, and examples of using plug-ins for DITA specializations and the FO plug-in extension point. The training aims to help users customize DITA-OT processing through the use of plug-ins.