Laboratoire d ’ Analyses et Modélisation de Systèmes pour l ’ Aide à la Décision UMR 7243

The paper aims at addressing the problem of what makes specific aiding to decide within public policy making problem situations. Under such a perspective it analyses some basic concepts such as “public policy”, “deliberation”, “legitimation”, “accountability” and shows the necessity to expand the concept of rationality which is expected to be behind the acceptability of a public policy. We then analyse the more recent tentative to construct a rational support to policy making, that is the “evidence-based policy making” approach. Despite the innovation introduced with this approach, we show that it basically fails to address the deep reasons for which supporting the design, implementation and assessment of public policies is a hard problem. We finally show that we need to move one step ahead, specialising decision aiding methodology to meet the policy cycle requirements: a demand for policy analytics.