ActionScript is a scripting language owned by Adobe. It is based on ECMAScript, and is used primarily for the development of websites and software using the Adobe Flash Player platform (in the form of SWF files embedded into Web pages), but is also used in some database applications (such as Alpha Five), and in basic robotics, as with the Make Controller Kit. Originally developed by Macromedia, the language is now owned by Adobe (which acquired Macromedia in 2005). ActionScript was initially designed for controlling simple 2D vector animations made in Adobe Flash (formerly Macromedia Flash). Later versions added functionality allowing for the creation of Web-based games and rich Internet applications with streaming media (such as video and audio).

Initially focused on animation, early versions of Flash content offered few interactivity features and thus had very limited scripting capability.

More recent versions include ActionScript, an implementation of the ECMAScript standard which therefore has the same syntax as JavaScript, but in a different programming framework with a different associated set of class libraries. ActionScript is used to create almost all of the interactivity (buttons, text entry fields, drop down menus) seen in many Flash applications.

Flash MX 2004 introduced ActionScript 2.0, a scripting programming language more suited to the development of Flash applications. It is often possible to save time by scripting something rather than animating it, which usually also enables a higher level of flexibility when editing.

Since the arrival of the Flash Player 9 alpha (in 2006) a newer version of ActionScript has been released, ActionScript 3.0. ActionScript 3.0 is an object oriented programming language allowing for more control and code reusability when building complex Flash applications.

Of late, the Flash libraries are being used with the XML capabilities of the browser to render rich content in the browser. This technology is known as Asynchronous Flash and XML, much like AJAX. This technology of Asynchronous Flash and XML has pushed for a more formal approach of this technology called Adobe Flex, which uses the Flash runtime to build Rich Internet Applications.

This technology can be used in players like those on MySpace and YouTube, to provide protection for the content that the Flash calls, like MP3s and videos. The content called is streamed through the Flash files, making downloading for storage a difficult task for most people. Programs such as Real Player Downloader and browser extensions like Firebug can trace the XML files.