Users can request xbooks from the xbook server through a xbook client. We provide two xbook clients: a portlet and a command-line client. The portlet is a GUI client and is targeted to the end-user who needs to be guided through the process of how to invoke a xbook. While the command-line client is targeted to Grid programmers who often need to invoke a xbook with a specific configuration in a single keystroke during debugging and development. Each client is described in the following sub-sections.