Life-span developmental psychology includes a broad array of principles that have wide application to studying adult development and aging. Three principles have guided my past, current, and future research: (a) development being a cumulative, lifelong process with no one period taking precedence; (b) multiple processes influence development (e.g., age-, pathology-, nonnormative, and mortality-related processes); and (c) development is multidirectional and multidimensional. This paper elaborates on how these principles have guided my research studying resilience to adversity across the adult life span and how my research aligns with guiding elements of resilience across definitions and literatures. I also discuss my current and future research of applying these principles to studying resilience in midlife, which emphasizes how the defining features of midlife lend themselves to examining resilience, midlife continues to not be well understood, midlife health foreshadows health in old age, and the experience of midlife will evolve in the context of an increasingly diverse society. The last section elaborates on additional directions for future research, such as the promise of intensive longitudinal research designs that incorporate qualitative approaches and examining historical changes in midlife health and well-being. In conclusion, a life-span developmental psychology framework has wide application for elucidating the nature of resilience across the adult life span through the integration of its principles with existing paradigms and research designs that blend contemporary methods with mixed methodology.