This document provides an introduction to Mule, an open-source enterprise service bus (ESB). It discusses what Mule is, how it can be used, and its core concepts. Mule uses technologies like staged event-driven architecture (SEDA) and Java NIO to facilitate integration. Core Mule concepts include endpoints, routers, filters, transformers, and the universal message object (UMO). The document also provides examples of using Mule for file processing and XML pipelines. It demonstrates how Mule handles normal processing as well as exceptions.