This thesis has been prepared in a paper based format and comprises of three stand-alone papers. Paper 1, a systematic review; Paper 2, an empirical study; and Paper 3, a critical appraisal and reflection of the work.Paper 1 has been prepared for submission to Appetite. The paper presents a systematic literature review of studies measuring or reporting potential psychological mechanisms within Night Eating Syndrome (NES). Databases were systematically searched and 20 studies were included in the review. The quality of evidence was mixed and NES was identified and diagnosed in a variety of ways. Studies utilised a variety of different instruments to identify thirteen psychological mechanisms. Syntheses of the studies suggest that there are distinct overlapping features within these mechanisms and five overarching themes were identified to accommodate these overlapping features. Suggestions are made relating to the potential function of the identified psychological mechanisms within NES.Paper 2 has been prepared for submission to Appetite. The paper is a qualitative study exploring the relationship between NES and the experience of emotion specifically from the perspective of patients identified as obese. Ten participants were interviewed and a constructivist grounded theory approach was used to analyse transcripts. A key category to emerge from the analysis was termed 'Emotional Hunger'; reflecting an urge or need to satiate a set of underlying unmet emotional needs. 'Emotional hunger' was underpinned by the following six interrelated themes: (1) The development of a relationship with food; (2) Loss; (3) The significance of night time; (4) A separation of the body and mind; (5) Why I eat, not what I eat; and (6) Consequences of night eating. The clinical implications of the findings are discussed with reference to existing literature.Paper 3 is not intended for publication. The paper provides a critical review of the research process, in which the strengths and weaknesses of the systematic review and empirical study are discussed. Personal and professional reflections on the experience of conducting a systematic review and an empirical study are explored. The clinical implications of the research are also discussed.