Over half of all Veterans suffer from stress-related illnesses; of particular concern is PTSD. In addition to supporting post-deployment stress treatment, it is critical to integrate stress inoculation training pre-deployment to teach proper coping mechanisms and prevent the PTSD cycle from starting. A challenge with developing such training is the objective, real-time monitoring of stress across trainees. Current methods for stress monitoring are laboratory-based (not mobile), and episodic in nature (e.g. self report). Wearable physiological sensors provide a quantitative assessment of stress (such as heart rate variability and electrodermal activity); however, the main challenge with these technologies is the lack of robust algorithms to classify stress in a mobile environment in real time. Physiological sensors are often activated by other inputs such as temperature and physical activity, and individual differences (e.g. age, gender, health status) and daily activities (e.g., physical movements, environmental changes, caffeine intake) pose a complex problem in achieving an accurate classifier. A review of several stress monitoring algorithms published in literature has been conducted and applied to a study designed to collect the high quality data necessary for modeling and development of a classifier that accurately detects stress in a mobile environment in real-time. The study procedures, results, and development of this algorithm are outlined, including use of unobtrusive hardware and robust logic to disseminate between psychological stress and physical activity. Although the main objective of developing a mobile classifier using non-invasive sensors to classify stress with over 85% accuracy was achieved, further refinement is needed to maintain the high level of accuracy across a variety of users and environmental conditions. Future research will include further accuracy refining through reduction in environmental noise and a smart algorithm to learn individual user stress thresholds. Applications for this research within the military and others are discussed.