Functionalism has been one of the most influential intellectual traditions in the development of psychology, anthropology, and sociology. This entry explores its philosophical foundations, disciplinary expressions, and theoretical projections. In psychology, it played a key role in the emergence of a science focused on adaptation; in anthropology, it shaped the analysis of institutions; and in sociology, it evolved into neofunctionalism. Special attention is given to its reformulation within systems theory. The aim is to provide an integrated and updated synthesis that acknowledges both the explanatory potential and the limitations of functionalist thought in current epistemological debates.