Context can be defined as all factors that are not part of a quality improvement intervention itself. More research indicates which aspects are 'conditions for improvement', which influence improvement success. However, little is known about which conditions are most important, whether these are different for different quality interventions or whether some become less or more important at different times in carrying out an improvement. Knowing more about these conditions could help speed up and spread improvements and develop the science. This paper proposes ways to build knowledge about the conditions needed for different changes, and to create conditional-attribution explanations to provide qualified generalisations. It describes theory-based, non-experimental research designs. It also suggests that 'practical improvers' can make their changes more effective by reflecting on and revising their own 'assumption-theories' about the conditions which will help and hinder the improvements they aim to implement.