Rohner has dedicated his professional life to researching interpersonal (especially parental) acceptance-rejection issues throughout the lifespan. His work has led to the development of interpersonal acceptance-rejection theory (IPARTheory). The theory is composed of three subtheories, each of which deals with a separate but interrelated set of issues. Specifically, IPARTheory’s personality subtheory—which is the most highly developed component of the theory—deals primarily with the pancultural nature and effects of interpersonal (especially parental) acceptance and rejection.Coping subtheory explores the fact that some individuals are better able to cope with experiences of perceived rejection than are other individuals. Finally, IPARTheory’s sociocultural systems subtheory attempts to predict and explain major causes and sociocultural correlates of interpersonal acceptance-rejection worldwide. Empirical evidence overwhelmingly supports the theory’s major postulates and predictions, especially postulates and prediction in personality subtheory. Emerging evidence about the neurobiological and biochemical risks posed for the development, structure, and function of the human brain are beginning to help explain why these postulates and predictions are so consistently confirmed panculturally. IPARTheory and associated measures have roots in almost six decades of research with more than 200,000 children, adolescents, and adults in over 60 nations worldwide, and with members of every major American ethnic group. Currently, IPARTheory has 25 measures available translated into 53 languages and dialects for assessing interpersonal acceptance-rejection.