The enduring importance and utility of comparative research in sociology are as old as the discipline itself. Although comparative research flourishes within this discipline, methodological problems persist. After defining comparative research, this article outlines some of its central problems, including: (1) case selection, unit, level and scale of analysis; (2) construct equivalence; (3) variable or case orientation; and (4) causality. The discussion finishes with a brief introduction of the critical and innovative articles within this special issue that not only address these problems, but also present promising solutions. © International Sociological Association.