Parliamentarism, a political system based on the principle of the division of power, in which the legislature has a parliament, consists of several basic constitutional features that will be explicated through this graduate thesis. This kind of system in today has become the key political figure of most states in the world. Hence, the parliamentary government system is a form of a system that implies the government's acting as an executive authority based on parliamentary elections or consensus. Thus, the aim of the paper is to clarify the basic concepts related to the parliamentary government system, and to achieve it, it is necessary to conceptually and generally define the principle of the division of power, constitution and constitutional rule, and to classify the perception of constitutional models of governmental organization. In accordance with the above, the work is divided into six units. The first ensemble includes introductory remarks, while others outline the general features and theories of government structure. Furthermore, the third part included the classification and the features of the constitutional model of organization, that is, the government organization. The fourth part of the work is precisely defined and understood by the parliamentary government system, its development through the past as well as the explication of its features. Considering that the area covered will not be completely unresponsive to the concrete example, the fifth unit of work will analyze constitutional organization, correlation, governmental organization on the example of the Republic of Croatia before and after 2000. Sixth chapter as the last one brings final considerations according to the subject of graduate thesis.