Numerous theories of depression have been proposed and tested with several variables being implicated in the etiology of unipolar depression in the last 15 years. The time has come for unification and integration of recent depression research. Four characteristics of the preunified theory of depression include: (1) failure of researchers to relate their findings to the existing knowledge base resulting in a less than optimum cross-fertilization of specialties of psychology; (2) the premature abandonment of hypotheses which fail to account for all cases of depression; (3) unnecessary restriction of theory and research approaches to particular methodologies; and (4) failure of many theorists to acknowledge the similarity of their ideas to the contributions of others. A paradigmatic behavioral theory of depression promotes an integrative, unifying paradigm of our knowledge of depression. This theory is designed to encourage an end to fragmentation by its integrative and not eclectic nature. Determinants of depression are proposed which can be understood within the context of well-established principles of classical and operant conditioning. As a base for this theory, a philosophy of science entitled unified positivism is employed. The evaluation of this paradigmatic behavioral theory of depression has just begun, but continuing research is planned. (ABL)