Two aspects of Vico’s constructivist epistemology are germane to contemporary cognitive developmental psychology. These aspects are Vico’s account of cognitive operations and of the limits to human knowledge of the world. Drawing on Vico’s epistemological treatise, and on contemporary commentary on Vico, it is argued that this eighteenth-century constructivist epistemology is useful in two ways. First, by being a consistent, and so radical, constructivism it may be helpful in clarifying the meaning of the environment in Piaget’s theory. Second, the description of mental operations may provide a way of overcoming objections to the overly formal quality of Piaget’s basic concrete-operational structures.