Self-management is a dynamic process of self-regulation by a person to manage the day-today consequences of living with long-term physical conditions (LTPC). Emerging adulthood, the transition between adolescence and adulthood, is a time of optimism with many life transitions, that brings different challenges and responsibilities. Arnett’s Theory of Emerging Adulthood identifies five distinctive features of this developmental stage: identity exploration, instability, self-focus, feeling in-between, and possibilities. Across three studies, this research aimed to examine do emerging adults with and without LTPC differ in the distinctive features of emerging adulthood, and how do these features influence selfmanagement behaviours among those living with LTPC. The first study, a systematic review of 30 papers found that emerging adults living with LTPC experience the five features of emerging adulthood within the context of their self-management, but that emerging adulthood can pose distinctive challenges to successful self-management, highlighting a need for comparative, quantitative research between emerging adults living with and without LTPC. Consequently, the second study, a secondary analysis of the Growing Up in Ireland dataset (n=4788), examined and found differences in those living with LTPC and their peers on factors linked with the five features of emerging adulthood. The third study, a cross-sectional survey (n=642) specifically examined Arnett’s features of emerging adulthood in emerging adults living with and without LTPC and the relationship between emerging adulthood and self-management for those living with LTPC. Whilst emerging adults with LTPC experience emerging adulthood similarly to their peers, those with higher levels of instability reported a lower ability to self-manage their condition. This thesis provides valuable evidence that for emerging adults living with LTPC, the developmental stage of emerging adulthood can act as a risk factor for the self-management of their LTPC. These findings can inform future research, healthcare practice and government policy.