This thesis addressed the question of whether global, 'executive' control processes are involved in switching between discrete cognitive tasks. The involvement of executive working memory processes in the control of switching was examined, using a combination of cognitive and cognitive neuropsychological methods. In all studies, participants switched unpredictably between two simple tasks, and in some cases they also performed concurrent tasks. The focus throughout was on two putative areas of executive control that may influence task switching, goal-directed advance processing, and the suppression of interference between tasks. The first series of experiments explored whether the central executive of working memory is required to prepare for a task switch, but found no evidence that this is the case, whether an endogenous or an exogenous method of task cueing is used. The possibility was then raised that cognitive control does not just operate when the task switches, and a further study showed that this is, indeed, the case. However, two experiments using different task cueing methods did not reveal any evidence that executive processes in working memory carry out this control. It did, however, appear that the central executive is required for overall task performance, as opposed to task switching, when the method of cueing requires that participants keep track of and update information about which task is to be performed. The final study examined task switching and executive function in a group of patients with damage to the frontal lobes, and to posterior areas of the brain. Although a number of participants showed evidence of executive deficits, they had no difficulty in switching in a speeded response task. In conclusion, it is argued that local, rather than global, control processes are involved in switching tasks in the present paradigm, and implications are discussed for theories and investigation of executive control. 2