This chapter explores the biopsychosocial factors that influence prescribing behaviour. It begins by introducing theories of behaviour to explore how health systems, pharmaceutical companies, individual professions, roles and identities, colleagues, patients, the time of day, personal beliefs, habits, emotions and the environmental setting can all influence prescribers and their prescribing behaviour. It also discusses the influences of wider society and culture and how that has also shaped healthcare, prescribing practice and patients’ understandings of illness and their expectations around healthcare and treatment. Having taken a look at all these influences on prescribing behaviour, it gives an overview of interventions that help prescribers optimise their prescribing decision making and prescribing behaviours as well as optimise patient satisfaction with and adherence to treatment. These include person-centred and shared decision making, using motivational interviewing to enhance communication during consultations and evidence-based training programmes that have used these approaches to optimise non-medical prescribing.