Most user interface development methodologies have been conceived based on the experience from the development of traditional PC-based systems. However, computer and displays technology is changing. The size spectrum now ranges from large surrounding displays to small mobile devices. Besides, 3D graphics is no longer limited to graphics workstations, as most PCs are shipped with specialized hardware, and 3D standards are being developed for mobile devices. User interface engineering should not be left out his progress. With that concern in mind, the IDEAS methodology is presented, a novel environment which allows the development of both 2D and 3D user interfaces for a wide range of devices. A case of study is used to show the details of the proposed development process.