Abstract. We present and discuss a formal, high-level approach to the specification and composition of interaction protocols for service-oriented systems. This work is being developed within the SENSORIA project as part of a language and formal framework supporting the modelling of complex services at the business level, i.e. independent of the underlying platform and the languages in which services are programmed and deployed. Our approach is based on a novel language and logic of interactions, and a mathematical semantics of composition based on graphs. We illustrate our approach using a case study provided by Telecom Italia, one of our industrial partners in the project.