Scientific evidence continues to accumulate that relates the experience of stress with overall poor health. However, defining what is meant by the term ‘stress’, in-order to examine its association with the experience adverse health, has been a difficult task for medical researchers. In the present investigation, using linear mixed effect regression analyses, we were interested in evaluating how the experience of psychosocial stress was related to one conceptualization of ‘stress’ as it impacts the human body, allostatic load. Allostatic load, proposed as ‘the cost of chronic exposure to fluctuating or heightened neural or neuroendocrine response resulting from repeated or chronic environmental challenge that an individual reacts to as being particularly stressful’ has been identified in the medical literature as mechanism that is associated with numerous negative health events, especially with regards to overall worse cardiovascular and immune system health. Our aim was to identify the extent to which a cumulative measure of psychosocial stress was related to allostatic load, as well as, identify the relative contributions of eleven specific dimensions of stress to that relationship. We also evaluated whether and how these relationships were moderated by sociodemographic, health behavior and psychosocial resource characteristics, to better understand how psychosocial stress was related to allostatic load across various sub-populations. Data for the analyses were obtained from the Midlife Development in the United States (MIDUS) study, a national, longitudinal investigation with a purpose to investigate the role of the behavioral, psychological and social factors that account for the age related variations in health and well-being across a national sample of Americans. As presented within the written dissertation, further information is provided for readers as an overall introduction to the dissertation (Chapter 1), additional details regarding our proposed aims (Chapter 2), the background and significance for our line of inquiry (Chapter 3), the analytical methods that were implemented for the purpose of this investigation (Chapter 4), the results and findings from our analyses (Chapter 5), a discussion of the results and findings (Chapter 6) and then a highlight of the main study limitations (Chapter 7) along with our overall study conclusions (Chapter 8).