Determinants of antibiotic prescribing in primary care in South Africa: studying patient-provider interactions in the private and public sectors Because it increases the morbidity and mortality of bacterial infection, as well as the duration and cost of antibacterial treatment, antibiotic resistance constitutes a significant threat to global public health. The problem is even more critical in low- and middle-income countries which have higher infectious disease burdens, often higher rates of antibiotic resistance, less access to diagnostic tools, and fewer financial resources to purchase newer more effective antibiotics. In South Africa, antibiotic resistance is particularly high, despite an effective drug regulatory system and various initiatives to tackle the problem. Antibiotic resistance is accelerated by the overuse and over-prescription of antibiotics, which is the product of complex interactions between providers' decisions and knowledge, and patients' expectations. Yet research on the determinants of prescribing behaviours from LMICs in general, and South Africa in particular, is limited, and has been criticised for being too descriptive and superficial, with limited insight into the relative importance of different behavioural determinants to be able to prioritise interventions. In South Africa, most research efforts have focused on hospitals rather than primary care, despite the fact the majority of antibiotics are prescribed in primary care, mostly for respiratory infections.  This study aims to explore how the interactions between providers and patients influence inappropriate antibiotic prescribing for URTIs in public and private primary care in South Africa.  The study will include three components. First, drawing on medical anthropology, we will explore qualitatively providers' and patients' perceptions an experiences of antibiotic prescribing. This will be done through observations of consultations, interviews with providers and focus group discussions with patients. Second, building on the first part and drawing on methods from marketing research, we will design a survey consisting of a series of hypothetical clinical cases where clinical and patient characteristics will be systematically varied; for each case, the providers taking part will be asked indicate what drugs they would prescribe in a list of proposed drugs. The results will allow us to quantify the relative importance of the factors influencing antibiotic prescribing, with a view to inform policy-makers design future interventions. Finally, drawing on recent economics and medical education research, we will move beyond observational research and design a small randomised field study to test the impact of patients' knowledge and financial incentives on the prescribing practices of public and private primary care providers. This will be achieved with the use of standardised patients, who are healthy subjects trained to portray specific symptoms and disclose a rehearsed medical history. These patients will be sent to visit providers who agreed to take part in the research, at a time and under an identity unknown to them. The standardised patients will only differ in their expectations of antibiotics and the insurance status they will disclose. This will allow us to test the impact of these different characteristics on the likelihood of antibiotic prescription.   We anticipate that the results will provide invaluable insights into our understanding of prescribing decisions in the public and private sector in South Africa, thereby informing the stewardship programmes for antimicrobial resistance in this country. Beyond this setting, these findings will be useful to other middle-income countries with a similar mix of public and private providers. More generally, we aim to produce high-quality research and develop innovative methods that could be replicated in other low-income settings to study antibiotic prescribing. The Global Challenges Research Fund (GCRF) supports cutting-edge research to address challenges faced by developing countries. The fund addresses the UN sustainable development goals. It aims to maximise the impact of research and innovation to improve lives and opportunity in the developing world.