The significance of the motivational determinants of animal and human behaviour has been recognized for some time by psychologists, ethologists and other students of behaviour. The diversity of mechanisms and processes which have been proposed as explanations of motivated behaviour reflects the depth and complexity of this issue. In recent years, researchers interested in designing artificial creatures and similar robotic devices have turned to these theories of motivation as a means of making their creations more adaptive to real-world situations. This paper outlines some of the pertinent strands of motivation research in animal psychology and animal behaviour; topics considered include ethological models of motivation and psychological accounts such as drive theory and incentive motivation. These theories provide the framework for a review of artefactual models which include a motivational dimension in artificial neural and other parallel distributed animat control mechanisms. The paper goes on to explore the potential of an interactive view of motivation, adopted by theorists such as F. Toates (1986, Motivational Systems, Cambridge: Cambridge University Press), as the basis for identifying the problems of including a motivational dimension in the design of artificial creatures, e.g. the issue of 'emergent motivation'.