As to research and theory, Baltes was interested in advancing a life-span view of human ontogenesis that considers behavioral and cognitive functioning from childhood into old age using a family of perspectives that together specify a coherent metatheoretical view on the nature of development. Other substantive topics included work on historical cohort effects, cognitive development, a dual-process conception of lifespan intelligence, and the study of wisdom. His interests also included models of successful development and the cross-cultural comparative study of self-related agency beliefs in the context of child development and school performance. Together with his late wife, Margret Baltes, he proposed a systemic metatheory of ontogeny which characterizes lifespan development as the orchestration of three processes: selection, optimization, and compensation.