The primary aim of the Stress and Activity Study was to ascertain both the effect of momentary stress perception on whether an individual engages in exercise, and whether engaging in exercise in turn influences the subsequent perception of stress among 79 healthy adults. The acute and chronic stress that individuals encounter in their lives each day can interfere with the adoption and maintenance of good health practices, including regular physical activity. Conversely, regular physical activity can reduce the harmful health effects of acute and chronic stress while improving emotional well-being and the ability to withstand stress. Thus, it is apparent that stress and physical activity impact each other and their relationship is bi-directional in nature. Using advances in mobile health technology, this was the first study ever designed to document the bi-directional relationship between personalized stress and exercise behavior in real-time over an extended-period. With the collection of minute-by-minute objective physical activity data (via Fitbit) and the assessment of perceived stress and stress sources 5 times per day (via smartphone text-messages) for 365 consecutive days, along with a comprehensive baseline assessment period and weather data, numerous research questions outside of the primary study aims can be examined at the within-person (e.g. n of 1) and between-person level using this rich dataset. Collaborations are welcomed and encouraged.