Current Infrastructure as a Service (IaaS) clouds operate in isolation from each other. Slight variations in the virtual machine (VM) abstractions or underlying hypervisor services prevent unified access and control across clouds. While standardization efforts aim to address these issues, they will take years to be agreed upon and adopted, if ever. Instead of standardization, which is by definition provider-centric, we advocate a user-centric approach that gives users an unprecedented level of control over the virtualization layer. We introduce the Xen-Blanket, a thin, immediately deployable virtualization layer that can homogenize today's diverse cloud infrastructures. We have deployed the Xen-Blanket across Amazon's EC2, an enterprise cloud, and a private setup at Cornell University. We show that a user-centric approach to homogenize clouds can achieve similar performance to a paravirtualized environment while enabling previously impossible tasks like cross-provider live migration. The Xen-Blanket also allows users to exploit resource management opportunities like oversubscription, and ultimately can reduce costs for users. © 2012 ACM.