This paper seeks to understand policy in the City of New York which limits cooperation with federal authorities for purposes of immigration control. It does so by qualitatively analyzing a set of legal-administrative documents. The key, policy features are identified along with the interests and forces which shaped those features over time. An arsenal of supplemental, legal material as well as the findings of legal scholars are consulted for interpretation in hermeneutic fashion. Using a theoretical framework consisting of the structure of the legal system of the United States and it norms, plus certain immigration-related, national trends, this research concludes this policy is the legacy of an unbroken, bi-partisan lineage of administrations dating back to the 1980s – an evolving product of the tensions between the legal norms and the national trends. The policy reinforces sovereignty from the federal government, and it does so largely for purposes of constitutionality, administrative functionality and civil rights.