This introductory guide draws on a number of key IUCN Red List of Ecosystems (RLE) papers, case studies and background documents to provide a practical introduction to the RLE. It targets those who wish to gain a deeper understanding of the RLE as a risk assessment tool and those who wish to learn more about its possible applications in implementing conservation action. This document draws heavily on Version 1 of the Guidelines for the application of the IUCN Red List of Ecosystems Criteria and Categories and provides an overview of the scientific foundations supporting the RLE categories and criteria.