This paper discusses the contributions to theoretical psychology of the late Professor Ludwig von Bertalanffy, a prominent biologist. Von Bertalanffy proposed open systems theory to explain life phenomena. Open systems, living organisms are examples of such systems, do not follow the second law of classical thermodynamics. They are characterized by negative entropy. This property explains organismic growth, differentiation and increasing complexity. It also explains goal directness, purposefulness and complexity of both human and animal behaviours. Consequently, von Bertalanffy has rejected reductionism and "atomism' which have characterized both the American Behaviourism and orthodox psychoanalysis. Instead, he has emphasized the organismic and holistic approach. He has also emphasized the unique peculiarities of human behaviour such as symbolism and creation of values. Symbolic and value systems have played a more important role in human motivation than biological drives. The influence of von Bertalanffy's general systems theory has gone beyond biology, it has extended to psychology, psychiatry, sociology, cybernetics and philosophy. Using the general systems theory framework von Bertalanffy has attempted to reconcile the natural scientific approach to human behaviourism with the humanistic one.