Religiosity is a concept used to describe numerous aspects of religious beliefs and doctrine. The aims of this thesis were twofold: the initial aim was to explore the concept of religiosity and its influence on the psychological process of coping, both general coping and religious coping. This offers a client perspective on the influence of religiosity in a person's life. The second aim was to explore how religiosity is addressed from a clinical psychologists' perspective in therapy. This first aim was achieved by conducting a qualitative systematic review on the relationship between religiosity and coping in people with a chronic illness. Secondly, an qualitative interpretative phenomenological approach was used to explore the experiences of clinical psychologists in relation to how they have addressed religiosity in clinical practice. The results showed that religiosity has a significant positive effect on coping, which indicates that higher religiosity, coping strategies such as social support, positive religious coping and active-cognitive coping are utilised by individuals to help manage a chronic illness. Furthermore, how religiosity is addressed in clinical practice is influenced by the clinical psychologists' professional identity, which enabled clinicians to adopt a non- judgemental approach influenced by their awareness of religiosity and beliefs. Creativity and the utilisation of religious resources were identified as factors that helped take account of client's religious beliefs in therapy. However, one consideration was whether professional training enabled religiosity to be addressed. It was concluded that the measurement of religiosity is not a simple task, varying aspects of religiosity need to be measured concurrently to give an overview of the person's religiosity. As the different aspects can influence a person's coping in different ways, which has the potential to affect outcome. Moreover, the results highlight the importance of religiosity being addressed in clinical practice and within clinical training.