This document provides an overview and introduction to a guide for assessing the quality of democracy. It discusses the global spread of democracy in recent decades and the need for valid ways to measure and evaluate democratic progress. The International Institute for Democracy and Electoral Assistance (International IDEA) developed an assessment framework that moves away from external rankings and focuses on comprehensive self-assessments led by governments and civil societies. The framework considers democratic principles, values, and performance questions. It has been applied successfully in over 20 countries. This revised guide incorporates lessons learned and experience to provide tools for assessing and promoting democratic reform from within societies.