A brief overview of the history of the orienting reflex (OR) in western psychology is presented, in order to provide a context for a discussion of its role in attentional processing. Some aspects of observed response fractionation are discussed, leading to an outline of a coherent theory of preliminary processes in OR elicitation. This discriminates between involuntary and voluntary aspects of cognitive processing but depends on a common core mechanism. The role of state variables in modulating phasic responses is also discussed. Although this theory was developed largely from a study of autonomic responses, it has been possible to extend it to include various central measures, and recent extensions are described. A number of recent studies are briefly outlined to provide examples demonstrating the use of a range of physiological measures (central and peripheral) in a variety of situations (from the pistol range to the laboratory) with different subject groups (adults, children and psychiatric patients). Finally, the use of heart rate data in the investigation of task-relevant cognitive load is discussed as a relatively simple but sensitive index to explore drug and other effects in cognition. These examples indicate the wide-ranging potential benefits of using psychophysiological approaches in the study of cognitive processes.