Policy making in health is largely thought to be driven by three ?I?s namely ideas, interests and institutions. Recent years have seen a shift in approach with increasing reliance being placed on role of evidence for policy making. The present article ascertains the role of ideas and ideologies in shaping evidence which is used to aid in policy decisions. The article discusses different theories of research-policy interface and the relative freedom of research-based evidence from the influence of ideas. Examples from developed and developed countries are cited to illustrate the contentions made. The article highlights the complexity of the process of evidence-based policy making, in a world driven by existing political, social and cultural ideologies. Consideration of this knowledge is paramount where more efforts are being made to bridge the gap between the ?two worlds? of researchers and policy makers to make evidence-based policy as also for policy analysts.