To support the deployment of ubicomp systems, the ubiquitous computing research community has developed a variety of middleware platforms, meta-operating systems and toolkits. While there is evidence that these systems share certain abstractions, it is not realistic to use the same platform in all environments; systems and applications specialized for specific environments and applications will always be required. In this paper we present a methodology for interoperability that allows developers to innovate and evolve their platforms while allowing others to build interoperable applications. Our approach is based on our design of the Ubicomp Common Model (UCM) and an implementation of this model called the Ubicomp Integration Framework (UIF). Our aim in this work is to provide clear evidence that the UCM unifies the capabilities of ubicomp systems based on an evaluation and analysis of its use in integrating several existing systems into a composite campus environment.