An innovation system is aimed at developing, diffusing and using innovations. Since a nation or a country represents a relevant level of analysis, the national innovation systems were first considered. However, there can be different types of innovation systems. In order to analyze an innovation system, it is necessary to identify the functions of the respective system or the determining factors of the innovation processes within the respective system. The flaws of a national system can only be emphasized by comparing the system with other existing national innovation systems. An innovation system can never reach a balance because of the evolutive feature of the innovation processes. The state and the public innovation agencies can influence the functioning and evolution of the national innovation system by means of the public innovation policy.