This thesis concerns exploring and understanding loneliness and connectedness amongst service users in acute adult mental health inpatient care, through a qualitative study using grounded theory. The empirical study used a constructivist grounded theory approach to explore the subjective experiences of loneliness and connectedness for service users both immediately before and during an admission to an acute adult mental health inpatient unit. Six service users with a diverse array of psychiatric symptoms were interviewed. Their constructions of how they experienced loneliness and social connectedness were coded with a focus upon identifying actions and processes. Three major categories emerged: (1) factors changing connectedness,(2) responses to changing connectedness and emerging processes, and (3) responding to inpatient care. The small sample size limits the generalisability of these findings. These categories may help identify valuable social processes to consider in acute care, and support further investigations in this area. A narrative literature review evaluated the state of research regarding the subjective experience of loneliness and an area relevant to acute care, the onset of psychosis. The review identified that research has begun to explore whether loneliness may directly or indirectly influence the onset of psychosis, but is currently limited both by the cross-sectional nature of studies, and a lack of understanding of how the construct of loneliness might be different for people with psychosis. A need for further research across more diverse populations is highlighted in a third paper, along with other research and clinical implications.