 <p>AIR addition to the actionscript 3 language that provide ways to control features from windows, mac, and linux. eg the titlebar and saving files.</p> <p>Flex is an addition to the actionscript 3 language that provides way to new interrogation features from server technologies like java, php, asp and connection between multiple flash applications and databases.</p> <p>Flash (CS4) can include AIR code but doesn't include Flex code. the server technology in Flash is limited but exists. Flash includes the GUI that stream lines developing. Like vector based graphics, filters, and components. Also more documentation and examples because it's easier to rewrite classes from Flex into Flash then rewriting Flash code for classes.</p> <p>Where in Flash you have a button, radio button, dropdown, or menu for every property of a movieclip, image, button. Where in Flex you can write all these properties/options by simply copying pasting, and tweaking the raw code.</p>