The availability of virtualization features in modern CPUs has reinforced the trend of consolidating multiple guest operating systems on top of a hypervisor in order to improve platform-resource utilization and reduce the total cost of ownership. However, today's virtualization stacks are unduly large and therefore prone to attacks. If an adversary manages to compromise the hypervisor, subverting the security of all hosted operating systems is easy. We show how a thin and simple virtualization layer reduces the attack surface significantly and thereby increases the overall security of the system. We have designed and implemented a virtualization architecture that can host multiple unmodified guest operating systems. Its trusted computing base is at least an order of magnitude smaller than that of existing systems. Furthermore, on recent hardware, our implementation outperforms contemporary full virtualization environments.