XenServer uses the same licensing process as other Citrix products. XenServer requires a License Server. For details on how to install and run Citrix Licensing, see Citrix eDocs website.
After purchasing support for XenServer you will be provided with .LIC license key. This license key should be installed on either:
XenServer Licensing is dependent on the version of XenServer you have installed on your host. Refer to the following table to know more about licensing concepts in various versions of XenServer.