Background: There is research evidence to support the growing recognition that leadership influences successful improvement; also that it is one factor explaining slow, partial or failed improvement. However, the evidence is not strong, especially about how important one or more leaders actions were compared with other situational factors. Methods: This paper summarises the evidence found in a review of research into different leader's roles in quality improvement. Results: Actions suited to the situation and type of improvement appear to be the most successful, and this has implications for developing leaders to 'fit' their actions to their situation and the improvement, and for research to help them do this better. Conclusions: The full review lists other practical implications for leaders where there is good evidence, and notes other literature which could provide guidance for leaders in the absence of research. It also considers the limitations of the research, and specific subjects for future research where knowledge and practical guidance for leaders are especially needed.