Sometimes, a single cloud isn’t enough. Sometimes, you need the whole sky. That’s why a number of researchers are developing tools to federate clouds, an architectural concept dubbed “sky computing” .The Sky Computing model allows the creation of large scale infrastructure using resources from multiple cloud providers. These infrastructures are able to run embarrassingly parallel computation with high performance. Developing a way to join several cloud infrastructures together into one massive cloud would be especially useful to academic researchers who utilize open large-scale compute resources, like the Open Science Grid or the European Grid Infrastructure, together with open source cloud computing platforms such as Nimbus, in order to create their own private clouds with rather than say Amazon’s EC2. In this paper we talked about sky computing and differences between grid, cloud and sky computing. and various mechanics that might lead to sky computing over multiple clouds, and then that idea was picked up by many projects.