Optimal cognitive development is defined in this article as the highest level of cognitive function reached in each cognitive domain given a person's biological and genetic disposition, and the highest possible maintenance of cognitive function over the adult life course. Theoretical perspectives underpinning the development of a framework for understanding optimal cognitive development are described, including differential development, intra-individual dynamics, cascades, biological mechanisms, reserve capacity, and plasticity. The Cognitive Health and Environment Life Course Model (CHELM) is proposed as a means to provide a framework for understanding the socio-demographic, lifestyle, and health factors influencing cognitive development and decline. The CHELM may guide framing of policy and interventions to optimize cognitive development and minimize cognitive decline in late-life.