The diversity of today?s computing devices has increased the difficulty of cross-platform application development. Multi-Device Authoring Technology (MDAT) is an end-to-end development methodology and toolset for building interactive, form-based Web applications that run on multiple devices. In this article, the authors describe how their approach to multidevice application authoring minimizes the incremental cost of supporting new devices and maximizes the flexibility for device-specific customization. MDAT provides an integrated visual environment for specifying a device-independent generic application and for customizing it for specific devices. The customization process is semiautomatic, which lets developers augment automatically generated code at key points in the process. Additionally, MDAT provides a visual generalization tool that translates legacy HTML pages into MDAT's generic representation. MDAT?s architecture also includes runtime adaptation, which dynamically generates device-specific versions of applications on Web servers to handle requests from new devices.