In 1977, Engel published the seminal paper, "The Need for a New Medical Model: A Challenge for Biomedicine" [Science 196 (1977) 129-136]. He featured a biopsychosocial (BPS) model based on systems theory and on the hierarchical organization of organisms. In this essay, the model is extended by the introduction of semiotics and constructivism. Semiotics provides the language which allows to describe the relationships between the individual and his environment. Constructivism explains how an organism perceives his environment. The impact of the BPS model on research, medical education, and application in the practice of medicine is discussed.