This paper highlights the importance of research synthesis for healthcare managers' and policy makers' questions and the difficulty of generalizing from the methods used to answer clinicians' questions. Social science research has a central role in such syntheses because of the context-dependent nature of managers' and policy makers' questions, which generally encompass a far broader spectrum than the circumscribed "what works?" questions of clinically oriented reviews. A major challenge is in moving from purely researcher-driven processes, which summarize research, to co-production processes, which allow managers and policy makers to join with researchers in interpreting implications for the healthcare system. Additional challenges lie in clearly defining the function, role and objective of the synthesis; handling flexibility around finalizing the question; harnessing a manageable scope of literature to review; adopting rules to select the final sample of research; creating useful messages; and developing a format that is responsive to the needs and preferences of the audience. One inevitable conclusion is that research synthesis for managers and policy makers will, compared to that for clinicians, leave much discretion in the hands of the synthesiser(s). This raises the interesting issue of how to engender, in the absence of "methodological checklists," trust and credibility in both the people doing the synthesis and the processes they use.