An observational tool was developed to measure guardianship potential and guardianship in action in residential areas in The Hague, the Netherlands by Reynald (Crime Prevention and Community Safety 11(1):1-20, 2009; Journal of Research in Crime and Delinquency 47(3):358-390, 2010). Guardianship potential was measured using the defensible space-based measures from the Block Environment Inventory (BEI), while Guardianship in Action (GIA) was observed by recording whether or not guardians (1) were visibly available, (2) were monitoring, and (3) intervened when necessary. This article reports on an international comparison of GIA in The Hague and in an American city. A comparative understanding will help advance knowledge on the measurement of active guardianship and related defensible space dimensions and identify socio-cultural differences in the application and meaning of the guardianship concept. Key results include that the observable dimensions of guardianship in action were reliable and valid, but some differences existed between the two sites including significant differences related to the social interaction measure. Similarities and differences across the two sites are examined, and implications for theory and research are explored.