In June 2006, ActionScript 3.0 debuted with Adobe Flex 2.0 and its corresponding player, Flash Player 9. ActionScript 3.0 was a fundamental restructuring of the language, so much so that it uses an entirely different virtual machine. Flash Player 9 contains two virtual machines, AVM1 for code written in ActionScript 1.0 and 2.0, and AVM2 for content written in ActionScript 3.0. ActionScript 3.0 provides not only a significant enhancement in performance, but also a more robust programming model that lends itself to complex Rich Internet Application development.

The update to the language introduced several new features:

* Compile-time and runtime type checking-type information exists at both compile-time and runtime.
* Improved performance from a class-based inheritance system separate from the prototype-based inheritance system.
* Support for packages, namespaces, and regular expressions.
* Compiles to an entirely new type of bytecode, incompatible with ActionScript 1.0 and 2.0 bytecode.
* Revised Flash Player API, organized into packages.
* Unified event handling system based on the DOM event handling standard.
* Integration of ECMAScript for XML (E4X) for purposes of XML processing.
* Direct access to the Flash runtime display list for complete control of what gets displayed at runtime.
* Completely conforming implementation of the ECMAScript Fourth Edition Draft specification.