Political regime is a mode of organizing and functioning of a political system. To state the matter differently it is the totality of methods and procedures used by power in the process of governing. The essence of political regime, its form of expression in social practice is the result of relations between classes, parties, political fractions mirroring the level of civil rights and freedoms that exist in a state. Without insisting on opinions about the definitions and typology of political regime, we shall analyze its evolution from the perspective of constitutional law basing on the distinction of legislative and executive function as well as explanation of their cohabitation. The only necessary precision is the fact that if occasionally some elements of political regime contradict these of the form of governing or state structure, herewith they do not lose identity or originality of political regime defining aspects. Thus, the nature of political regime is defined by the relation between a particular regime and citizens. From the very beginning of constitutional life political regime has become regularized in definite juridical forms, evolving gradually from one historical period to another. The phenomenon of continuous development and improvement of state constitutions has indisputably proved the permanent enhancement of constitutional norms and provisions referred to unwritten demands emerging in a society life.