Psoriasis is an immune-mediated chronic dermatological condition associated with a range of physical and psychological comorbidities, and a significant disease burden. Healthy sleep plays a key role in maintaining health and wellbeing. Conversely, chronic sleep disturbance significantly increases the risk of developing a range of physical and mental health conditions if left untreated. Sleep disturbance is a known feature of other chronic conditions and is associated with disease-specific influences and consequences. Therefore, given the links between sleep, health and functioning, the experience of sleep disturbance in psoriasis was investigated using a multi-method approach. Chapter One provides an overview of psoriasis and sleep and the potential impact psoriasis and sleep disturbance can have on health and wellbeing. Chapter Two identifies what is known from the existing literature and the limitations of the studies reviewed. From here a prospective research agenda was formulated. A cross-sectional survey (Chapter Three) sought to address the gaps in the literature by examining the extent, characteristics and correlates of sleep disturbance using validated measures. Chapter Four then describes the first in-depth qualitative study exploring the experience of sleep disturbance in people with psoriasis. The Common-Sense Model of Self-Regulation was used as a guiding framework and facilitated exploration of beliefs, emotions and behaviours associated with sleep disturbance. This study provided insights into the role of psoriasis specific factors, the impact of sleep disturbance on daily life and the limited coping options available. Using Experience Sampling Methodology, Chapter Five examined the bi-directional and sequential relationships between sleep disturbance and daytime variables in psoriasis. Multiple daily assessments of psoriasis, mood, night-time experiences and functioning were combined with actigraphy and sleep dairies. This study revealed possible treatment targets to improve sleep and daytime functioning. However, findings related to psoriasis were contrary to previous chapters. The findings from the preceding chapters were synthesised in Chapter Six. The methodologies used were also critically appraised. Clinical implications were discussed in addition to a brief overview of potential avenues for future research.