The need to share resource and data across organizational boundaries is fundamental and wide-spread. As more organizations move their IT system an on-demand and mobile environment, it is clear that system security boundaries will be software-defined. Sharing data and resources, then, means securely bridging those security domains. This is what federation does.In this era of cloud computing, machines, storage, and networks have all been virtualized. Federation, in essence, provides a virtual administrative domain wherein stakeholders can jointly agree on the goals, policies, and operation of the federation. Federation -- as virtual administrative domains -- is the logical next step in managing collaborations with potentially a global footprint.