Any notion or concept of stress should fulfil the following requirements. First, the definition should be readily communicable both to professionals and the community at large. Second, the concept should be readily converted into constructs which are suitable for research. In this latter regard it is easier to present and discuss a stress model. This model differentiates a number of factors which, although interdependent, are conceptually distinct. By adequately discriminating between these factors, operational criteria may be defined and a systematic assessment of the effects of stress will be facilitated. A model is thus presented which describes the stress process.