The problem of reconciling the subjectively known mind with the objectively known brain has puzzled philosophers and scientists for centuries. When attempting to solve this problem in recent times, the focus has been on explaining how the mind is born from the brain, how the two are related, and how we can best understand them. This problem is of particular relevance to clinical psychology because it attempts to both understand and explain pathological presentations by appealing to both subjective personal experience and objective knowledge of the physicality of the brain. In this respect, clinical psychology straddles the gap between mind and brain. This thesis investigates the implications of the mind/brain problem for theory and practice in clinical psychology. Chapter one identifies the tension between knowing the world subjectively and knowing the world objectively and discusses the importance of understanding this tension when investigating the mind/brain problem. Chapter two sets out the foundational concepts of cognitive behavioural approaches in clinical psychology, looking in particular at how cognitive behavioural approaches conceptualise mental events like thoughts and beliefs. It is concluded that while cognitive behavioural approaches to clinical psychology regularly incorporate both mentalistic and physical concepts in its theory and practice, it does not address the inherent problems in their combined use, as revealed by the mind brain/problem. In order to improve the use of mentalistic concepts within the theory and practice of cognitive behaviourally based clinical psychology, chapter three explores the major conceptualisations of mind from the discipline of philosophy of mind. To achieve this improvement, chapter four, suggests that refining of mentalistic concepts in clinical psychology, through the application of philosophical concepts of mind, can be made possible through the use of a framework that captures the different explanatory levels at which the mind/brain operates. The levels-of-explanation framework is put forward for this purpose. Of particular relevance to clinical psychology is the ability to retain the importance of autonomous, subjectively experienced, and causally efficacious mental events, while at the same time, being able to give a realistic account of how these mental events are linked to the physical brain. The levels-of-explanation framework is judged to be a suitable approach with which to achieve this. In chapters five and six, the implications of clinical psychology's use of mentalistic concepts are explored in relation to evidence-based practice and case formulation. It is shown that through a greater understanding of both the nature of mind and the relationship between the mind and the brain, improvements can be made to both the theory and practice of cognitive behaviourally base clinical practice. This is achieved through the application of philosophical concepts of mind, via a levels-of-explanation framework, while both researching and undertaking clinical practice in clinical psychology.