Unlike his ideas about education and philosophy, John Dewey's psychology has been largely neglected. This article begins the rediscovery of his transactional psychology by seeking a synthesizing reading of those of his works that pertain to psychology. The article first outlines his transactional approach and also his metapsychology, which conceived of psychology as involved in the constitution of its own subject matter. Then some central psychological concepts such as habit, thinking, self, mind, meaning, and consciousness are explained within the transactional framework, and some similarities are highlighted between Dewey's psychology and ecological psychology. It is argued that Dewey's psychology is still very relevant in the 21st century.