Although cloud computing enables developers to cost-efficiently access compute and storage, it is not yet an undifferentiated commodity (like telephony) since each cloud provider offers proprietary services. To make progress towards a vision of utility computing (where applications can run on any cloud without any changes), Ion Stoica and Scott Schenker propose “Sky computing” – motivated by the design of the Internet. Their concept of Sky computing includes a compatibility layer to reconcile low-level technical differences among cloud providers; an intercloud layer to route jobs to the right cloud-based on policies specified by users but without requiring low-level decisions about job placement; and a peering layer of economic agreements on how clouds may exchange payments for services.