Achieving the Millennium Development Goals has proven to be a real challenge. Providing evidence on cost-effective interventions did not prove to be sufficient to secure the trust of national authorities, health care providers and patients. Introducing change in a health system requires a good understanding of the relationships between the actors of the system. Social network analysis can provide a new avenue to analyse the diffusion of innovations within a health system or a health organisation and analyse the structure and the properties of a health system. Evidence has been generated on the necessity of not only identifying the actors of a system but also qualifying the relationships between these actors.