ClearPath systems are increasingly participating in environments where they collaborate with other systems, within the same organization or externally. Service–Oriented Architecture (SOA) is now seen as providing a well–structured architectural framework for building these distributed applications. This paper outlines the architectural ideas behind SOA and explains the role of middleware as the enabling technology. It then reviews Unisys middleware strategy and describes the middleware products available with ClearPath OS 2200 systems, categorized by middleware type. The main body of the text summarizes the key features of the products available, with a number of technical briefs providing more detail about the technology and products. Some examples show how ClearPath OS 2200 systems are being used in distributed architectures.