The objectives of the present paper are to describe selected findings from a research project on the diffusion and adoption of innovations in primary-care settings. The project design was a comparative case study design exploring four innovations in different settings. The findings are used to explore the influence of evidence on clinical behaviour, particularly how clinical professionals judge credible evidence and take decisions. The article goes on to explore other influences on behaviour and the role of context in shaping processes and behaviour. Finally, the concluding section draws out the relevance of these data for the current changes being implemented in primary care, and raises questions about the implementation of clinical governance and quality improvements.