Scholars of Comparative Politics investigate similarities and differences in patterns of politics across the world. They engage in within-country, cross-national, and cross-regional research with a geographic focus outside the United States (although the US may be included as a case in cross-national comparative research). Comparativists use a variety of methods and often possess deep expertise in particular countries or regions. This knowledge is important for the purpose of systematic comparison, theory building, theory testing, and awareness of context specific variables and causal relationships masked by immersion in our own polities and societies. The field of Comparative Politics includes, among others, the study of political institutions and regimes; electoral behavior and procedures; identity, ideology, and culture; public policy; political economy; political violence; social movements and organizations; and protest and revolution.