American psychiatry transformed dramatically between 1945 and 1980. From psychoanalytic dominance beginning during the immediate postwar period, a new diagnostic psychiatry, its near theoretical and practical antithesis, came to dominate by the end of the period, as it has to the present. This paper provides a field-theoretical account of this transformation. The practical fit between forms of practice and the demands of the field are crucial to the account. Using field theory, my account also stresses the relationship between meaning and practice, and the residues of the objectified histories of fields and the incorporated histories of the actors who both comprise and change them. I illustrate these concepts with an account of the transformation of psychiatry, and I conclude by critiquing the systems approach to institutional change in the professions developed by Andrew Abbott. I also draw links between field theory and more general accounts of institutions and institutional change.