Several vendors produce virtualization technologies today. Some of the most commonly used products are Microsoft Hyper-V, VMware vSphere, and Citrix XenServer. All these vendors offer a fairly similar base feature set with some unique features on top. In relation to Lync Server 2013, Microsoft certifies particular hypervisor products for use in order to be supported. Today, only the Microsoft Windows Server 2008 R2 Hyper-V, Microsoft Windows Server 2012 Hyper-V, and VMware vSphere 5 are certified for use with Lync Server 2013. Additional vendors can work with Microsoft later to achieve certification. This chapter focuses on the Microsoft and VMware hypervisors because they are the two supported platforms at this time.