Research-based evidence has the potential to influence health policy making, but its impact is contingent on a number of factors. Past analyses have underscored the role of politics in shaping policy choices, reflecting the nature of the social learning process and access of political forces at every stage of the policy continuum from agenda formation to policy enactment and implication. This article focuses on the mechanisms of the research evidence enterprise itself, delving directly into what influences the pathways of research evidence into policy making, taking into consideration both the production and consumption functions of such evidence. It presents a process model of the role of research evidence in policy making, examining in conceptual detail variations in the production of evidence in the research community; the communication of policy-relevant results through translation, framing, and other means; the methods of acquisition of the evidence by policy makers and their advisers; and the multiple ways in which evidence is put to use in policy decision making. I use examples from health care reform to illustrate features of the process model.