The so-called sanctuary cities are currently the main source of opposition to federal anti-immigrant policies in the United States. The central argument of this cross-case study is that the sanctuary category brings together a set of informal laws, policies and practices of different nature, with diverse political origins and varying degrees of insurgency. That article argues that an in-depth study of the context of each type of sanctuary may explain the existence of such a contrasting spectrum. Three representative categories within the spectrum are proposed to differentiate them: rhetoric sanctuaries, de facto sanctuaries and welcome sanctuaries. This study concludes that the most representative sanctuary practices — with greater insurgency and scalability — are linked to the city’s need to defend its access to funds and protect its political autonomy; but also the ability of organised migrants to build alliances with local political actors.