In this article an attempt is made to intruduce briefly the central concepts of general systems theory and communication theory and to illustrate their application to psychiatric thinking. The review is mainly based on publications of authors such as Bateson, Jackson, Haley, Watzlawick and others connected with the Palo Alto Mental Research Institute. After explaining the concept of man as an 'open system' and the principle of 'wholeness', a model of the family as a homeostatic unit of individual subsystems, governed by feedback, is presented. The principle of 'equifinality' implies the usefullness of studying present interactions rather than relying exclusively on historical explanations for the comprehension of psychiatric symptoms.