On January 25, 2017, President Donald Trump signed Executive Order 13768, which marked the first federal action targeting American sanctuary cities and fulfilled one of Trump’s key campaign promises. Sanctuary cities, which do not permit local officials to inquire into immigration status and may decline ICE detainer requests, have been in existence since the early 1980s, but the shooting of Kathryn Steinle in 2015 brought them renewed attention. Ms. Steinle’s accidental shooting by an undocumented immigrant, Jose Ines Garcia Zarate, ignited a firestorm of controversy over these policies. Garcia Zarate had been released by the SFPD based on San Francisco’s sanctuary policy, leading then-candidate Donald Trump to make a promise to “end” sanctuary cities a key part of his campaign for president. Yet many Americans know very little about sanctuary policies despite their growing importance in the debate over undocumented immigration and the incorporation of immigrant communities. In this work, Drs. Collingwood and Gonzalez O’Brien provide the first comprehensive examination of sanctuary cities in the United States. Analyzing the historical evolution of these policies, the tone and tenor of media coverage, public opinion, state-level sanctuary legislation, and the effect these policies have on crime rates and Latino political incorporation, the authors hope to provide researchers, members of the public, and lawmakers with the tools to objectively assess the value of sanctuary legislation.