The recent demand for new measures of the rule of law confronts several methodological challenges. This article calls for careful attention to fundamental social science ideas of conceptualization and measurement in approaching the rule of law. Efforts to measure complex social phenomena such as the rule of law are challenging, and thus require that researchers and policy makers pay attention to the cautionary rules of social science in their efforts. Violating these basic rules risks producing measures that are not reliable or valid, and could be a bad basis for policymaking. This paper demonstrates some of the pitfalls that rule of law researchers have fallen into and suggests improvements in measurement approaches.