This thesis considers the concept of involuntary action in the criminal law. In particular it examines the defence of automatism. The discussion of the defence by the courts in England and Wales and jurisprudential commentary regarding involuntary action are considered. Present legal definitions of involuntary action do not take account of current scientific or philosophical debates relating to consciousness and the science of the mind. It is argued that modern neuroscientific definitions of consciousness are useful to the criminal law. They suggest how consciousness is used by the brain to assist in the carrying out of tasks and to monitor the interaction between the individual and the world in which her behaviour takes place. They provide evidence that conscious awareness of tasks differs according to the complexity of the task undertaken and the experience of a particular person in performing a particular task. On this view conscious awareness will exist in varying degrees according to the task which is being undertaken and the person performing that task. It is argued that a purely mechanistic or reductionist evaluation of consciousness will not assist in defining criminal responsibility. The thesis also examines differing types of explanation of action. These include philosophical definitions of action and discussions of how consciousness relates to action. The opinions of courts in five other jurisdictions on certain approaches to the automatism defence are considered. The problems of combining legal and philosophical definitions are discussed. A revised test of involuntariness is suggested. The research findings contribute to the fund of knowledge in a number of ways. Firstly they review the case law of automatism in England and Wales and certain aspects of the defence of automatism in five other jurisdictions. Secondly the research examines the relevance of modern neuroscientific research and the philosophy of consciousness in relation to the criminal law's approach to involuntary action. Finally the research findings are utilised to propose a new test of involuntariness.