Communication is based on messages intended to provide their recipients with a new perception of reality and thus to alter their behaviour. For the public administration, communicating is therefore an indispensable means to achieve its ends, which are often fixed by general norms. The complexity of the functions performed by the public administration also affect its communication. Simplifying, it si possible to single out three principal communicative modalities: communication in order to regulate, communication in order to serve, and communication in order to convince. Communication-to-regulate is the most frequently used and serves to apply norms to and among those who belong to the order. Communication-to-serve furnishes general and specific information to users, and is in itself a service. Communication-to-convince seeks to explain, sensitize and responsibilize (and therefore convince) citizens regarding "system problems", that is to say, issues that require a joint effort by all subjects in order to achieve goals of general interest.