Increasing attention has been paid in recent years to efforts to strengthen the impact of research on policy in low- and middle-income countries. However, the processes by which such research might have policy impact remain a subject of debate. This paper presents an analysis of the research/policy interface, drawing on the experiences of two South African health policy and systems research (HPSR) units and one specific study which traced the development and implementation of three areas of health care financing policy change and debate between 1994 and 1999. The analysis is based primarily on the authors' own experiences and has been developed through a deliberate process of reflection. It suggests, first, that it is important to acknowledge the conceptual and symbolic uses and impacts of research--perhaps, particularly in relation to the system-oriented work of HPSR groups. These uses may not be verifiable by specific changes in policy and practice but are important contributions to the policy environment and do filter into policy-makers' understandings and actions. Second, achieving any form of impact on policy is linked to the attention researchers pay to the context in which the research is undertaken, the nature and credibility of the research; and the importance of nesting any single project in a broader programme of engagement with the policy environment that builds trust in the researchers.