Handheld mobile technology is reaching first responders and soldiers in the field to help with mission execution. A characteristic of mission execution environments is that people are typically deployed in teams or groups to execute the mission. Most commercially available, context-aware mobile applications are based on context expressed mainly as location and time of an individual device plus the device user’s preferences or history. This work extends context to consider the group that the individual is a part of and presents a reference architecture for group-context-aware mobile applications that integrates contextual information from individuals and nearby team members operating to execute a mission. The architecture is highly extensible to support changes in context data models, context data storage mechanisms, context reasoning engines and rules, sensors, communication mechanisms, and context views. A prototype implementation was built to demonstrate the validity and extensibility of the reference architecture. This work was presented at the 4th International Conference on Mobile Computing, Applications, and Services, Oct. 2012, and published in Lecture Notes of the Institute for Computer Sciences, Social Informatics and Telecommunications Engineering in 2013.