Abstract
This paper presents a review of recent studies of the human controller both in psychology and in control engineering. Theoretical and technological problems in the study of skilled behaviour are first discussed, and the desirable constraints upon any "model" are outlined. The foundations of linear continuous modelling of the human controller and experimental data on the validity and utility of linear models are then reviewed. The evidence for non-linear and discontinuous behaviour in the human controller is then outlined, and studies of non-linear models based on modern optimal and sampled-data control theory are then presented.