Wiley Acta Medica Okayama 17485983 15 2020 How Networks Among Frontline Offices Influence Regulatory Enforcement : Diffusion and Justification of Interpretation of Risk 1388 1405 EN Ayako Hirata Faculty of Law, Okayama University Street‐level interpretation and enforcement are critical to defining the meaning of law. To understand street‐level regulatory decisions, prior studies have highlighted internal office conditions, neglecting the influence that peer offices can have. This study examines the role of horizontal inter‐office interaction among frontline offices and illustrates how and under what conditions it shapes the meaning of law. Drawing on qualitative and quantitative data on Japan's Soil Contamination Countermeasures Act, this study reveals that inter‐office interaction occurs within fixed groups and comes to shape shared interpretations of law that regulators believe are legally valid. This implies that under legal ambiguity, inter‐office interactions develop institutionalized notions of appropriateness and reinforce the perception of legal consistency, which bolster the legitimacy of enforcement. Although peer office networks encourage convergence on the interpretation of law, because of their clustered structure, legal meanings develop differently across various groups. No potential conflict of interest relevant to this article was reported.