Comparative politics is a field in political science, characterized by an empirical approach based on the comparative method. In other words, comparative politics is the study of the domestic politics, political institutions, and conflicts of countries. It often involves comparisons among countries and through time within single countries, emphasizing key patterns of similarity and difference. Arend Lijphart argues that comparative politics does not have a substantive focus in itself, but rather a methodological one: it focuses on "the how but does not specify the what of the analysis." In other words, comparative politics is not defined by the object of its study, but rather by the method it applies to study political phenomena. Peter Mair and Richard Rose advance a slightly different definition, arguing that comparative politics is defined by a combination of a substantive focus on the study of countries' political systems and a method of identifying and explaining similarities and differences between these countries using common concepts. Rose states that, on his definition: "The focus is explicitly or implicitly upon more than one country, thus following familiar political science usage in excluding within-nation comparison. Methodologically, comparison is distinguished by its use of concepts that are applicable in more than one country."
When applied to specific fields of study, comparative politics may be referred to by other names, such as for example comparative government (the comparative study of forms of government) or comparative foreign policy (comparing the foreign policies of different States in order to establish general empirical connections between the characteristics of the State and the characteristics of its foreign policy).
Sometimes, especially in the United States, the term "comparative politics" is used to refer to "the politics of foreign countries." This usage of the term, however, is often considered incorrect.
"Comparative political science" as a general term for an area of study, as opposed to a methodology of study, can be seen as redundant. The political only shows as political when either an overt or tacit comparison is being made. A study of a single political entity, whether a society, subculture or period, would show the political as simple brute reality without comparison with another society, subculture, or period.