Across North America, Europe and Latin America, multiple sub-state jurisdictions have declared themselves to be migrant “sanctuaries”. By adopting sanctuary status, sub-state jurisdictions signal their welcoming attitude towards migrants as well their opposition to the state-level policies that target them for exclusion. In this article, I examine the place of sanctuary in the broader literature of political resistance and opposition in democratic states, and then whether it can be justified all things considered. I locate my examination in the political theory of federalism, to identify an expectation of cooperation – which, it appears, sanctuary jurisdictions are refusing to accept, usually with respect to immigration enforcement efforts. I refer to this form of opposition as “democratic non-cooperation” and identify its key features. I describe a “cooperation continuum”, to suggest that non-cooperation takes four main forms – evasion, non-engagement, disruption and obstruction – which I describe both in general terms and in relation to sanctuary practices in particular. Finally, I observe that the form of opposition that sanctuary is, is not limited to sanctuary: that is, there are other cases of this form of opposition in other policy domains, and moreover, not all of the objectives taken by those who deploy this form of opposition are progressive. Ultimately, this article's central contribution is to fleshing out modes of opposition in democratic spaces in general, by examining the morality of sanctuary actions taken around the world.