Administrative twinning projects are one of the instruments used by the preaccession strategy to adapt the candidate to the Copenhagen criteria. They settle up a relation between national administrations in old and new members, aimed to exchange know how, best practices and organizational models. In the field of judicial reforms the twinning have been used to finance activities address to build capacities and to change the organization of the judiciaries. The relations between old and new members, the supply of models and best practices put forward by the NGOs and the international think tanks and the appropriateness of the policy solutions proposed intervene as facilitating conditions in the process of diffusion of normative inputs. The paper analyses the mechanisms of selection and diffusion of know how and models and the conditions the twinning projects have created to foster the judicial cooperation in the enlarged Europe.