1. An interoperability network for facilitating access to a plurality of composite services by a plurality of users having associated client machines, each of the users being associated with one or more of a plurality of independent enterprises, the interoperability network comprising one or more computing devices configured to: provide a business application selection interface for selecting one or more of a plurality of pre-defined business applications, wherein at least some of the pre-defined business applications each comprises a composite service configured to integrate operation of a respective subset of a plurality of services in communication with the interoperability network; provide a composite service initiation interface for initiating an instance of a first selected one of the composite services, the first selected composite service integrating operation of a first subset of the services, the first subset of services being associated with and controlled by a first plurality of independent service providers; and connect with selected ones of the client machines and each of the services in the first subset of the services and selectively facilitate interaction among the selected client machines and the first subset of services, thereby enabling selected ones of the users to access the first selected composite service as an integrated solution in which the first selected composite service facilitates messaging between or among the first subset of services.