Methods and apparatus for an interaction system specifying cross-device interaction are provided. The interaction system provides application program interfaces (APIs) and a scripting environment that allow development of scripts that combine user input and sensing events and distribute output and across devices to create a range of rich cross-device behaviors with minimal development. The interaction system includes an integrated environment for developers to author and test cross-device behaviors. When a script is ready, the script can be deployed on a network of mobile and wearable computing devices using the interaction system's runtime environment. An interaction system script can. An evaluation of the interaction system with twelve participants revealed that the interaction system significantly reduced developer effort for creating and iterating on cross-device behaviors. The interaction system allowed developers to focus on target interaction behaviors and high-level device capabilities, rather than low-level specifications.