Sanctuary city policies seek to protect undocumented community members from federal detention or deportation. Debates over sanctu ary cities have become increasingly prominent and partisan in American politics. Republicans accuse sanctuary cities of enabling crime, while Democrats laud them for protecting communities from rights viola tions. Despite partisan salience, we have little information about peo ples' substantive knowledge of sanctuary policies or how crucial that knowledge is in shaping partisan attitudes toward those policies. Drawing on a unique survey dataset of sanctuary attitudes, we demon strate that an absence of political knowledge has asymmetrical effects on sanctuary attitudes along ideological and partisan lines. Knowledge about sanctuary policies increases support for sanctuary cities among liberals/Democrats, whereas conservatives/Republicans do not require substantive knowledge to align their attitudes on sanctuary cities with their ideological predispositions. This finding advances scholarship on the interplay between political knowledge and ideology, and has impor tant immigrationrelated policy and advocacy implications.Palabras Clave: ciudad santuario, política pública, opinión pública, políticas urbanas, conocimiento político.