Multimodal interfaces combining natural modalities such as speech and touch with dynamic graphical user interfaces can make it easier and more effective for users to interact with applications and services on mobile devices. However, building these interfaces remains a complex and high specialized task. The W3C EMMA standard provides a representation language for inputs to multimodal systems facilitating plugand-play of system components and rapid prototyping of interactive multimodal systems. We illustrate the capabilities of the EMMA standard through examination of its use in a series of mobile multimodal applications for the iPhone. Categories and Subject Descriptors H.5.2 [Information Interfaces and Presentation (e.g. HCI)]: User Interfaces—input devices and strategies (e.g. mouse, touchscreen),voice I/O. natural language, prototyping, standardization. General Terms standardization Keywords multimodal, standards, speech, gesture, prototyping