Evaluation, performance and management by results have driven the construction of quantitative data for following the implementation of public actions (measures, programmes, public policies). As decreed by the LOLF (Organic Law relative to the Financial Laws), all public action must hereafter specify its objectives and supply indicators intended to enable their monitoring and evaluation. Moreover, the demonstration of proving the efficiency or the pertinence of an action is all the stronger when it is supported by quantitative arguments. That statistical data is called upon to furnish arguments regarding public action is old news, what is newer is the extension of its use to domains thus far out of public statistics’ field, to all branches of managerial activity. The diffusion of managerial concerns accords great importance to figures, which questions those of statistics. This article reviews the fundamentals of statistics and the links it has to evaluating public actions in order to consider them in the new politico-administrative context (decentralisation and the revival of evaluation by constitutional laws).