Three aspects of the process of social change seem particularly to validate the application of social differentiation to the tumultuous development of public communication: 1. the ever more marked articulation of the institutions; 2. the growing awareness among citzens of their social and civil rights; 3. the development of mass communications. The assumption by the State of increasingly broader functions and its greater articulation have brought new institutions into being. These new institutions must develop horizontal communication among systems that grow more and more specialized. Mass schooling and greater information have heightened awareness of rights and increased the volume of demands advanced by individual citizens, associations and groups. They automatically entail the reinforcement of vertical communication, which has become more difficult because it must be more specific. The growth and specialization of horizontal and vertical communication has created new communication needs and also requires the development of new specialized skills.