This document provides an overview of the Xen API and how it can be used with JRuby. The Xen API allows for managing virtual machines and their resources through a standardized interface. It uses XML-RPC to expose methods that can be called from various programming languages. JRuby allows accessing the Xen API through Ruby code and RubyGems by wrapping the underlying C/C++ libvirt library. Examples are given showing how to connect to a Xen host, get information on VMs, and reboot a VM using the Xen API via Ruby code.