This document discusses enterprise application integration (EAI). It defines EAI as the unrestricted sharing of data and business processes among any connected applications and data sources in an enterprise. The document outlines EAI architectures including multi-tier architectures with presentation, application, and data tiers. It also discusses middleware, which allows communication across different platforms and between legacy and modern applications. The benefits of EAI include lower development and maintenance costs through looser coupling of systems and quicker integration.