This issue of Law & Policy adds to the growing body of empirical case studies of decision-making and enforcement in regulatory agencies. Summarizing that research, regulatory enforcement styles can be described in terms of two dimensions, one concerning the ways in which regulatory violations are defined and punished, the other concerning outcomes, described in policy-evaluative terms. In explaining variation in enforcement style, existing studies point to three sets of factors: characteristics of the regulatory “legal design”; features of agencies' “task environment”; and the regulatory “political environment.” Weighting the relative importance of these factors, however, is difficult because of the number and fluidity of variables and the adaptiveness of regulatory agencies.