Stress is nearly ubiquitous in everyday life, and imposes a tremendous burden worldwide by acting as a major risk factor of mental disorders, autoimmune, infectious and cardiovascular diseases, and some cancers. The aim of the FragMent project is to evaluate to which extent the spatial and temporal fragmentation of exposures to environments in daily life influences physiological and psychological stress, as well as social inequalities in stress. Some evidence shows that exposures to daily environments may either act as a stress contributor or provide some stress restorative qualities. While the protective effect of greenness has been clearly established, strong uncertainties remain regarding the effects of urban environments. FragMent starts from this premise to investigate the environmental determinants of momentary, daily and chronic stress in relation with immediate, daily and regular environmental exposures. The project uncovers the role of spatiality and temporality in exposure effects on stress. It further builds on the concept of space-time activity fragmentation, to contextualize patterns of exposure within activity patterns. Finally, it analyses how differences in space-time exposures and activity patterns across social groups may lead to social inequalities in stress. An observational cohort study will be used to evaluate momentary, daily and chronic stress in daily life, using a combination of traditional web-survey, map-based questionnaires, smartphone tracking and Geographic Ecological Momentary Assessment. A series of lab-based experiments, combining Immersive Virtual Environments with a walking simulator, will assess the effect of urban environmental characteristics and the temporality of exposures on momentary physiological and psychological stress. Bridging knowledge from epidemiology and time geography, FragMent will provide critical evidence to equitably reduce exposure to environmental stressors in outdoor space in everyday life.