In response to increasing concerns about quality, many countries are carrying out large scale programmes which include national quality strategies, hospital programmes, and quality accreditation, assessment and review processes. Increasing amounts of resources are being devoted to these interventions, but do they ensure or improve quality of care? There is little research evidence as to their effectiveness or the conditions for maximum effectiveness. Reasons for the lack of evaluation research include the methodological challenges of measuring outcomes and attributing causality to these complex, changing, long term social interventions to organisations or health systems, which themselves are complex and changing. However, methods are available which can be used to evaluate these programmes and which can provide decision-makers with research-based guidance on how to plan and implement them. This paper describes the research challenges, the methods which can be used and gives examples and guidance for future research. It emphasises the important contribution which such research can make to improving the effectiveness of these programmes and to developing the science of quality improvement.