1. A computer-implemented method for controlling access of Web service consumers to Web services available from Web service providers, the method comprising: receiving a request from a Web service consumer for access to an indicated Web service, the Web service being responsive to invocation requests and being available from a Web service provider in accordance with an indicated usage model, the indicated usage model having an associated use price and one or more associated use restrictions for the indicated Web service; automatically determining whether to authorize the requested access to the indicated Web service in accordance with the indicated usage model, the automatic determining being performed by one or more programmed computing systems and being based at least in part on whether the one or more associated use restrictions for the indicated usage model are satisfied by the received request from the Web service consumer and at least in part on whether payment for the use price of the indicated usage model is available; and if it is determined to authorize the requested access in accordance with the indicated usage model, automatically interacting with one or more remote computing systems of the Web service provider to invoke the Web service on behalf of the Web service consumer, the automatic interacting being performed by the one or more programmed computing systems and including sending one or more invocation requests to at least one of the one or more remote computing systems, the one or more remote computing systems being distinct from the one or more programmed computing systems.