Many diseases commonly associated with aging are now thought to have social and physiologic antecedents in early life. Understanding how the timing of exposure to early life risk factors influences later-life health may illuminate mechanisms driving adult health inequalities and identify possible points for effective interventions. Recognizing chronic diseases as developing across the lifecourse also has implications for the conduct of research on adult risk factors for disease. We review alternative conceptual models that describe how the timing of risk factor exposure relates to the development of disease. We propose some expansions of lifecourse models to improve their relevance for research on adult chronic disease, using the relationship between education and adult cognitive decline and dementia as an example. We discuss the important implications each of the lifecourse conceptual models has on study design, analysis, and interpretation of research on aging and chronic diseases. We summarize several research considerations implied by the lifecourse framework, including: advantages of analyzing change in function rather than onset of impairment; the pervasive challenge of survivor bias; the importance of controlling for possible confounding by early life conditions; and the likely heterogeneity in responses of adults to treatment.