Cloud Computing is a term applied to large, hosted datacenters, usually geographically distributed, which offer various computational services on a “utility” basis. Most typically the configuration and provisioning of these datacenters, as far as the services for the subscribers go, is highly automated, to the point of the service being delivered within seconds of the subscriber request. Additionally, the datacenters typically use hypervisor based virtualization as a technique to deliver these services. The concept of a cloud operated by one service provider or enterprise interoperating with a clouds operated by another is a powerful idea. So far that is limited to use cases where code running on one cloud explicitly references a service on another cloud. There is no implicit and transparent interoperability. Use cases for interoperability, as well as work-in-progress around inter-cloud protocols and formats for enabling those use cases, are discussed in this paper.