Since the beginning of the 1980's most industrialized countries have had to cope with the problem of managing the costs of their Health care systems and particularly the costs of hospitalization. The development of information technologies accelerated by the Internet have led to responses that depend greatly on the better management of information. Health care is entering the Information Society: the rise of networks is a key aspect of our Knowledge and Information Society. With information and services developments that allow for greater involvement of the patient, Health data and more particularly medical data represent a very important economic and social concern. This paper analyzes the rise of networks within the Health field from the French experience in Healthcare Networks and compares it with that of the United States, Canada, the United Kingdom and Spain. Then we outline the special properties of Health data: its personal, sensitive and confidential nature as well as how it needs to conform to particular legislation. Finally we study the use of these data, the essential role of Information and Communication Systems with its key element, the patient's Electronic Health Record, in promoting new practices based on information sharing and the quality of data. This marks the beginning of huge changes.