Chronic fatigue syndrome (CFS) describes a condition characterised by severe fatigue of at least six months' duration. In this thesis, it is argued that the complexity of CFS with respect to other symptoms, the patients' response to their illness and the determinants of emotional distress, has yet to be fully recognised. This may have narrowed the focus of research and limited the range of treatments available. The first of the three studies investigated CFS from the patients' perspective. The findings challenge some of the generalisations concerning CFS, particularly those relating to the patients' attributions and their choice of coping strategies. They also suggest that the effects of the condition may have been underestimated and that certain influences on emotional distress may have been overlooked. The second study assessed a number of variables thought to be associated with emotional distress and psychological adjustment. The results show that uncertainty and lack of social support were significantly correlated with anxiety and depression while functional impairment was more closely linked to cognitive difficulties and other illness-related measures. The third study evaluated a management programme which acknowledges the complexity of CFS. After six months, significant differences between the treated patients and waiting-list controls were found for a number of variables, including fatigue, somatic symptoms, anxiety and perceived self-efficacy. However, many patients continued to record high levels of emotional distress, showing that the programme was not sufficient to deal with all the problems experienced.