Simulations can be extremely successful in acquainting participants with a negotiation’s logic and process, especially in those political systems in which negotiations are prominent, such as the European Union (EU). After a brief introduction on the constructivist approach to teaching the European integration, in this paper we present step by step a simulation game on the adoption of a real piece of European legislation: the regulation that implemented the European Citizens’ Initiative, one of the main innovations of the Lisbon Treaty. Special attention is devoted to the different phases of a simulation design, from the choice of the topic, the choice and allocation of roles, the preparation of all needed documentations, to the debriefing and assessment phases. The paper originates from a two-years long experience with undergraduate students of two Italian Universities.