Interest in synthesizing the findings of qualitative and quantitative evidence is increasing in response to the complex questions being asked by healthcare managers and policy-makers. There is a wealth of evidence available from many sources--both formal research and non-research based (e.g., expert opinion, stakeholder, and user views). Synthesis offers the opportunity to integrate diverse forms of evidence into a whole. We categorize the current approaches to the synthesis of qualitative and quantitative evidence into four broad groups: narrative, qualitative, quantitative, and Bayesian. Many of the methods for synthesis are emergent; some have been used to integrate primary data; few have a long history of application to healthcare. In the healthcare context, synthesis methods are less well developed than methods such as systematic review. Nonetheless, synthesis has the potential to provide knowledge and decision support to healthcare policy-makers and managers.