In accordance with a few years of tradition, the present volume of «Studia Politologiczne» is devoted to the issues of political systems in the states of Eastern Europe, the authors being outstanding researchers of this region. The problems of political systems arouse unchanging interest of constitutional experts, theoreticians of the state and law as well as political scientists. This is not without a reason. The political system of the state determines all legal, political, social or economic relations occurring in its area, and as such it requires studies. The authors of the texts presented here submit different aspects of political systems of the states of Eastern Europe to analysis. They point to their dynamic character. They are not unchanging or established in the acts of law for good. It happens even when changes are not made in constitutional regulations, political frameworks, the political context of their application or the behaviour of the key participants of political relations. Sometimes, like it was the case in Armenia, these changes are of far-reaching, constitutional character and they include the form of government, which always requires in-depth analyses and observation as to whether they bring the desired effect.