While immigration enforcement in the US has often been the subject of heated debate, the question of how immigration law should be enforced and by whom has reached a fever pitch in the year since President Trump took office. Cities such as New York, Los Angeles, and Chicago, among others, have been labeled “sanctuary cities” based on their political and policy responses to immigration enforcement efforts by the current and past presidential administrations. In the past year, the tension between the Trump administration and these (and other) local governments has led to a struggle that is currently playing out in police stations, legislatures, and courts throughout the United States. The topic is a complicated one, and the laws around these cities are currently in flux, but we’ve put together a brief primer on so-called “sanctuary cities.”