<p>Frailty, generally characterized as a clinical state of increased vulnerability resulting from age-related decline in reserve and function across multiple physiologic systems, has been gaining attention in recent years due to its high correlates with a number of poor health outcomes including falls, hospitalization, and mortality. Although policy makers, health practitioners, and researchers have acknowledged that frailty is a major public health issue, few have investigated the life course predictors of this devastating and costly syndrome. The purpose of this dissertation is (1) to identify the early and later-life predictors of initial frailty and frailty growth over time among older US adults, (2) to examine if childhood exposures influence frailty directly and/or indirectly through adult risks and resources, and (3) to examine the role that social relationships play in frailty trajectories among older adults. Drawing from cumulative inequality theory, this dissertation uses longitudinal data from the Health and Retirement Study (HRS) to examine the effects of childhood exposures, adult risks/resources, and social relationships on frailty trajectories among adults 65 and older. The empirical investigation is presented in two main chapters.</p> <p>The first study investigates the life course predictors of frailty prevalence and further examines how childhood exposures may be directly and indirectly associated with frailty through adult risks and resources. The second study builds on the findings of the first by examining the predictors of frailty growth over time and investigating how social relationships in later life may shape that growth. Findings reveal each childhood exposure domain influences frailty either directly or indirectly through adult factors and experiences. Specifically, analyses reveal that childhood chronic disease, impairments, and risky adolescent behaviors directly influence frailty in later life. Additionally, results reveal that poor childhood SES was one of the most consistent predictors of adult frailty—but much of the effect was due to its influence on adult risks and resources. Few adult risk factors influence frailty trajectories over time. Among adult resources, socioeconomic status (particularly education) slows frailty growth over time. Finally, findings reveal that both social support and more social roles mediate the relationship between childhood exposures and frailty, and that the effect of more social roles continues over time. </p> <p>This dissertation highlights a number of life course predictors of frailty and identifies areas for potential interventions—particularly those aimed at providing equal access to higher education and quality social relationships over the life course. Most importantly, this dissertation demonstrates that frailty prevention should not be a task delegated exclusively to older adults. Effective prevention of this often devastating and costly syndrome should begin early in life.</p>