Over the last several chapters, you learned about creating and working with virtual machines (VMs). You also learned that, to facilitate some of Hyper-V’s advanced functionality, the guest operating system (inside a VM) must pass information to the hypervisor. Owing to the separation that virtualization provides, how does this process occur? A set of components, collectively called “Guest Integration Services,” provide this functionality. These services conduct several tasks, ranging from time synchronization and performance metric sharing to providing the ability to copy files from host to guest over the VMBus without requiring a network connection between the two. This short chapter explores these services.