In the sixties, tools were developed in France to test laws before they were adopted. This form of assessment found a constitutional basis with the Act of 28th March 2003 authorizing normative experimentation, both nationally and locally. This innovation was the gateway for a specific form of experimentation, randomized experiment, which borrows its methods from social sciences, and its perimeter from international policies on poverty. This form of experimentation raises three issues, which are discussed in three successive sections. The first one is a matter of legal science: what role does this form of experimentation play within the scope of normative experiments ? The second question is a scientific one: what lessons does social experimentation bring to experimental science applied to human behaviour ? The third issue is socio-political: what is its contribution to the evaluation of public policies ? The conclusion recalls the ethical and scientific requirements that are necesssary in the conduct and evaluation of experiments on human behaviour.