The flex applications are based on the Flash platform and it is a kind of RIA which includes Flash, actionscript and MXML based components. The AIR is more of a comprehensive platform which can be used to deploy the applications in desktop without the requirement of the Server/client framework as with Flash. The AIR can include all kinds of technologies including HTML, AJAX etc. The Flex applications are just one among the various other applications that can be deployed by the AIR. The AIR runtime has to be installed locally on the computer to run AIR application. Even with Flash present the AIR deployed Flex application may not run on the computer.