An extremely important factor in supporting and coordinating innovation activities in a country is the national innovation system. The objective of this paper is to research the role of the national, regional and technological innovation system in the development of the economies of low- and medium-income countries. The methodology of this study consisted first in the analysis of the specialized literature in the economic and managerial fields and the definition of the key concepts necessary for study of the national, regional and technological innovation systems. Then the sectors in the national innovation system are analyzed. It was identified stages that lead to an innovative economy, and which should be followed by developing countries. The results reveal the components of the national innovation system. Other results highlight the regional innovation system, its subsystems and basic functions. The sectoral and technological innovation systems reveal the industries which is part of them, and the relation between the two categories. We conclude the role of the national innovation system which creates an environment that supports the development of innovation at the national level.