Non-medical prescribers make an increasing contribution to healthcare across the UK yet little is known about influences on their prescribing decision-making. The aim of this programme of research was to explore and describe prescribing decision-making by non-medical prescribers. A two stage programme of research was carried out. Stage 1 was a systematic review of the social and cognitive influences on prescribing decision-making by non-medical prescribers. Despite a paucity of research, various influences on prescribing decision-making were reported including evidence based guidelines, peer support and patient (or parental) relationships and expectations. While confidence and clinical experience as a practitioner were cited as influences, the lack of prescribing experience and aspects of pharmacological knowledge also impacted on prescribing decision-making, resulting in a cautious approach. Stage 2 of the research employed a phenomenological methodology underpinned by the Theoretical Domains Framework of behavioural determinants (TDF). It comprised three phases. In Phase 1, semi-structured interviews with five nurse prescribers and eight pharmacist prescribers in NHS Grampian explored their experiences and perceptions of influences on their prescribing decision-making, and the impact of these influences. Multiple and sometimes contradictory influences were uncovered. Twelve of the fourteen domains of the TDF were found to be influential along with multi-disciplinary working and experience; optimism and reinforcement did not feature. In Phase 2, these participants recorded reflections on prescribing decisions which they considered noteworthy in relation to their practice, and in Phase 3 participants were interviewed about their reflections. Complexity was a feature of many, in the patients’ clinical or social circumstances or in relation to wider concerns. The same 12 domains were found to be influential as were multi-disciplinary working, experience and complexity. This programme of research has produced original findings which it is hoped will impact on the education, training and practice of these increasingly important prescribers.