Local and state governments in the United States pass sanctuary policies to limit their cooperation in dragnet immigration enforcement programs and to clarify for their frontline employees exactly how they should interact with immigration enforcement agencies. While typically seen as policy tools for protecting immigrants and resisting the federal government, in fact, these policies formally link local law enforcement agencies to federal immigration control systems, producing a form of “humanitarian” or pro-immigrant immigration detention and deportation assistance at the local level. Sanctuary policies prohibit the use of local resources - personnel, finances, data infrastructures, and detention space - for the purpose of assisting in the enforcement of federal immigration laws except in cases where individuals have a certain type of criminal conviction history or are being booked on certain criminal charges in local detention facilities. As such, sanctuary policies codify immigration enforcement assistance protocols to manage the detention and transfer of individuals in these cases, which end up being more frequent and routine than exceptional or occasional. While most accounts of sanctuary policies focus on the political battles surrounding them, the media narratives that form public opinion about them, or their legality within a federal constitutional legal framework, Border Criminologies research examining local law enforcement assistance to immigration authorities in sanctuary jurisdictions examines the mechanical aspects of on the ground policing, detention, information sharing, and immigration related custody transfers. It further examines the manner in which local law enforcement agents elaborate routine daily practices which facilitate immigration detentions and deportations in the process of implementing sanctuary policy-related department protocols and procedures.