AIMS: The aim of this study was firstly to reveal the determinants of GP prescribing behaviour for older adults in primary care and secondly to elicit GPs' views on the potential role for broad intervention strategies involving pharmacists and/or information technology systems in general practice. METHODS: Semi-structured qualitative interviews were carried out with a purposive sample of GPs. Three multidisciplinary researchers independently coded the interview data using a framework approach. Emerging themes were mapped to the Theoretical Domains Framework (TDF), a tool used to apply behaviour change theories. RESULTS: Sixteen GPs participated in the study. The following domains in the TDF were identified as being important determinants of GP prescribing behaviour: 'Knowledge', 'Skills', 'Reinforcement', 'Memory Attention and Decision Process', 'Environmental Context and Resources', 'Social Influences', 'Social/Professional Role and Identity'. Participants reported that the challenges associated with prescribing for an increasingly older population will require them to become more knowledgeable in pharmacology and drug interactions and they called for extra training in these topics. GPs viewed strategies such as academic detailing sessions delivered by pharmacists or information technology systems as having a positive role to play in optimizing prescribing. CONCLUSION: This study highlights the complexities of behavioural determinants of prescribing for older people in primary care and the need for additional supports to optimize prescribing for this growing cohort of patients. Interventions that incorporate, but are not limited to interprofessional collaboration with pharmacists and information technology systems, were identified by GPs as being potentially useful for improving prescribing behaviour, and therefore require further exploration.