philosopher and theoretical psychologist who exerted influence on American psychology during its formative period in the 1890s. Concerned with the relation of Darwinian evolution to psychology, he favoured the study of individual differences, stressed the importance of theory for psychology, and was critical of narrow experimentalism.

During a year of study in Berlin and at the University of Leipzig (1884–85), Baldwin became acquainted with the new experimental psychology and its founder, Wilhelm Wundt (Wundt, Wilhelm). To answer the need for English textbooks in the new psychology, he wrote a Handbook of Psychology, 2 vol. (1889–91). In 1889 he became professor of philosophy at the University of Toronto, where he established a psychological laboratory. Later, as professor of psychology and philosophy at Princeton University (1893–1903), where he established another laboratory, he published two works advancing evolutionary principles in psychology, Mental Development in the Child and the Race (1895) and Social and Ethical Interpretations in Mental Development (1897). With James McKeen Cattell, he founded the Psychological Review (1894), from which other publications also developed, including the Psychological Index and the Psychological Bulletin.

Baldwin edited the contributions of some 60 philosophers and psychologists in his Dictionary of Philosophy and Psychology, 3 vol. (1901–05), the final volume of which was a 1,200-page bibliography by Benjamin Rand. Associated with Johns Hopkins University, Baltimore (1903–09), he then spent five years in Mexico City as an adviser to the National University of Mexico. During this period he completed Genetic Logic, 3 vol. (1906–11), which examined the nature and development of thought and meaning. Settling in Paris (1913), he lectured at various provincial universities and in 1919 became professor at the École des Hautes Études Sociales in Paris.