The current thesis consists of a literature review and meta-analysis, and a research study. The literature review aimed to synthesise and summarise the hoarding disorder (HD) prevalence evidence base. A systematic search was conducted to identify all relevant studies. A random effects meta-analysis was then conducted, with subgroup moderator analysis and meta-regression. Eleven studies, comprising of twelve samples met criteria (n = 53,378). The pooled estimated prevalence for HD was 2.5% (1.7% to 3.6%). There was significant heterogeneity between studies, and subgroup analyses were inconclusive. Studies were predominantly from developed countries and were at low risk of bias. The pooled estimate of HD indicates that HD is an infrequently occurring diagnosis. Guidance on the manner in which HD is assessed in future prevalence studies is provided and the clinical implications of the results discussed. The research study aimed to explore emotions in participants prone to hoarding using Q-methodology. Forty-nine statements related to emotions in hoarding were generated following thematic analysis of two initial interviews. Forty-four participants (34 online, 10 offline) completed Q-sorts of the statements alongside a battery of psychometric measures. A by-person factor analysis was conducted and the clusters compared on the psychometric measures. Three participants failed to meet caseness for HD, a further seven failed to cluster. Four distinct participant clusters consisting a total n = 34 participants were identified: “emotionally overwhelmed” (n = 11); “social emotions” (n = 13); “object complexity” (n = 6); “object-affect fusion” (n = 4). The clusters identified did not differ significantly on measures of hoarding severity, anxiety, depression, and impulsivity. Complex emotions appear to be a significant component of HD. The four participant clusters elicited appeared to accurately reflect current research. This demonstrates significant emotional heterogeneity amongst people that hoard and so highlights the need for further research.