The growth of Internet has extended the scope of software applications, leading to network-based ar- chitectures. The main characteristic of these architectures is that they restrict the communication between remote components to message passing. Service-oriented computing is a solution to organise the exchange of messages in a network-based architecture, by using services as primitive components. Since a service- oriented application typically spans a number of different organisations, its execution is subject to stringent requirements at two levels : business and security. At each level, the requirements could be implemen- ted by a centralised control maintaining the correct interactions. But this solution is not realistic. Indeed, whereas each partner develops its own services, the whole application results from the collaboration of all the services in a truly concurrent way, without any centralised control. Thus, the partners involved gene- rally define a contract at the global level in order to enforce interaction policies, dealing with business and security functionalities. By the contract, they increase their mutual trust. From the contract, each partner deduces by projection a specification of the functionalities that it must locally implement. Of course, all these projections must ensure that the local functionalities, once gathered, effectively collaborate to realise the global contract. For each partner, it remains to realise the projection, by a local implementation.