Although the term “political regime” is widely used in political science, its definition remains vague, as is its relationship to the concepts of “state” and “government.” Also, despite the multidimensional nature of political regimes and their diversity in the real world, as a result of studies of democratic transition in recent decades, the main focus of the study and comparison of political regimes has been around the democracy-dictatorship dichotomy. This deficiency and shortcoming are more obvious in comparative politics studies. In order to address the existing deficiencies, the present article attempts to provide a precise and practical definition of the concept of political regime and also explains the relationship between the concepts of political regime, state, and government. After that, it explains the role of formal and informal rules and procedures in political regimes. Since political regimes are institutional in nature, the present article presents a multidimensional model for analyzing various aspects of political regimes within the framework of historical institutionalism. The six indicators of this analytical model are: state ideology, ruling elites, distribution of power within the state, state- society relations, state- market relations, and state’s international relations. Each indicator is assessed based on more detailed axes and components.