Our research into secure managed extranets was motivated by the requirements of companies (possibly competitors) needing to collaborate on occasion because transient business windows present mutual opportunities. Our contributions towards satisfying these requirements are twofold: (i) we present a service-construct abstraction based on what we term a ?Collaborative Context? where authorized participants (e.g. project leaders) have collective provisioning capabilities for the purpose of negotiating and contributing exclusive resources to create a virtual private enterprise, and (ii) we present a realization of the collaborative context as a commercially oriented, on-demand Virtual Private eXtranet Service (VPXS).