In this chapter, Wheaton and Montazer distinguish among commonly used terms for stress, stressors, and distress. They then examine models that have shaped our understanding of the stress concept, describing the ways in which the study of stress has evolved. The chapter begins by differentiating between two original models of stress: the biological stress model and the social engineering stress model. The authors then go on to define and differentiate different types of stress which lie within the “stress universe,” and consider the distinctions between different types (and sources) of stress. Beyond these conceptual distinctions is the empirical issue of whether we need to measure diverse sources of stress. Wheaton and Montazer argue that we do – and that we need to assess the “unique” effects of diverse sources of stress (controlling for other stressors) as well as the “total” effect of stressors on mental health. This point is illustrated with data from three studies. The chapter considers recent trends in stress research. The direction of research on stress since 2000 can be summarized by three points. First, many have focused on the combined effects of more than one type of stressor. Second, research has given considerable attention to the life course as cumulative differential exposure to stressors. The third trend focuses on social context and macro-stress. Compared to the earlier work on contextual stress that examined the role of economic downturns, recent research has focused more on natural and man-made disasters and mass violence. What are the unique sources of stress that we face today (as opposed to the stressors we faced twenty years ago), and how can we meaure these stressors as well as their effects?