Abstract How do city-level policymakers build support for substantive action in policy domains characterized by low levels of national salience and limited local capacity, and which evidentiary resources support as well as reflect these uses? Despite much attention to policymakers’ engagement with evidence, existing work tends to focus on domains where the issues at stake attract high levels of input and influence from central governments. This limits empirical and theoretical understanding of how local efforts to implement potentially contentious policies arise, and through which means. In response, we examine how municipal actors in 12 cities and regions across the UK have devised and communicated policies on immigrant integration—an area that lacks national policy inputs yet is locally consequential—through the mechanism of “action planning.” Drawing on 6 years’ worth of documentary evidence generated through a university-initiated collaboration with these municipalities, we show how action plans gather attention for objectives and propagate examples of practice to other cities—what we call “case-making.” This serves as a micro-foundation for the action planning mechanism, which links symbolic statements about immigrant integration with substantive intended actions.