Embracing service-oriented architectures in the context of large systems, such as the Web, rises a set of new and challenging issues: increased size and load in terms of users and services, distribution, and dynamicity. A top-down federation of service infrastructure support that we name “service cloud” and that is capable of growing to the scale of the Internet, is seen as a promising response to such new challenges. In this paper, we define the service cloud concept, its promises and the requirements in terms of architecture and the corresponding middleware. We present some preliminary proofs of concept through the integration of a JBI-compliant enterprise service bus, extended to our needs, and a scalable semantic space infrastructure, both relying on an established grid middleware environment. The new approach offers service consumers and providers a fully transparent, distributed and federated means to access, compose and deploy services on the Internet. Technically, our co...