This article presents a research method for assessing stress and mental health in ongoing population-based social surveys that combines self-reports of naturally occurring daily stressors with a primary marker of stress physiology, salivary cortisol. We first discuss the relevance of stress processes to mental health and introduce a model for examining daily stress processes, which highlights multiple components of daily stressor exposure. A primary aim of this approach is to capture variability across stressful situations, between persons of different groups, or within persons over a period of time. Next, we describe how the assessment of diurnal salivary cortisol is a promising approach to examining naturally occurring stress physiology in large social surveys. We then present findings from the National Study of Daily Experiences (a substudy of the Midlife in the United States Study) that document the feasibility and reliability of the collection of daily stressors and salivary cortisol and provide examples of research findings linking stressor exposure to cortisol. The final portion of the article describes ways that this approach can leverage the strengths of various features of longitudinal social surveys to extend research on stress and mental health. [PUBLICATION ABSTRACT] This article presents a research method for assessing stress and mental health in ongoing population-based social surveys that combines self-reports of naturally occurring daily stressors with a primary marker of stress physiology, salivary cortisol. We first discuss the relevance of stress processes to mental health and introduce a model for examining daily stress processes, which highlights multiple components of daily stressor exposure. A primary aim of this approach is to capture variability across stressful situations, between persons of different groups, or within persons over a period of time. Next, we describe how the assessment of diurnal salivary cortisol is a promising approach to examining naturally occurring stress physiology in large social surveys. We then present findings from the National Study of Daily Experiences (a substudy of the Midlife in the United States Study) that document the feasibility and reliability of the collection of daily stressors and salivary cortisol and provide examples of research findings linking stressor exposure to cortisol. The final portion of the article describes ways that this approach can leverage the strengths of various features of longitudinal social surveys to extend research on stress and mental health.