The quality and expenditure of prescribing have significant implications for patient care and public health and is therefore one of the top priorities within the NHS. However, influencing general practitioners' (GP) prescribing patterns have proved challenging. Resistance to change is influenced by issues such as the GP personal and professional experiences, the relationship with the patient and the perceived tension between primary and secondary care. The aim of this project was to investigate the significant influences on prescribing in two neighbouring Primary Care Trusts (PCT) using multiple methods taking a pragmatic approach. A questionnaire was designed to measure GPs' perceptions of prescribing influence in the two PCTs. From this study, a K-means cluster analysis grouped GPs according to their attitudes towards prescribing influence. Subsequent analysis of prescribing trends revealed that prescribing patterns were related to GPs' perceptions of prescribing influence. Relationships between national and local prescribing initiatives and prescribing trends were analysed and intervention analysis quantified the effects of prescribing change over time. These analyses showed that prescribing incentive schemes have a measurable effect on generic prescribing. Attitudes towards prescribing were further explored in-depth in interviews with GPs and stakeholders from the PCTs and the Health Authority (HA). The analysis exposed different perceptions and areas of potential conflict between stakeholders and GPs in regard to the prescribing agenda. The studies that comprised the thesis were triangulated in discussions on the influencing factors on prescribing. It could be concluded that GPs differed in their perceptions of the factors that influenced prescribing as well as their prescribing practice. The results imply that prescribing interventions need to be developed in line with the views of prescribers and policy makers. Additionally, these interventions should be tailored to different types of GPs holding different perceptions in order to optimise resource use and maximise prescribing change as and where appropriate.