States are uniquely situated as both individual governments in the federal system and entities that represent the interests of their citizens. So, what makes groups of states successful when they lobby the Supreme Court as amicus curiae filers? I argue that it is not just the number of states included in a coalition that matters, but rather which states are included. In this article, I offer a theory that implies certain types of coalitions will be more influential than others, as these coalitions can vary in how representative they are of public preferences. I use a dataset on state amicus curiae filings from 1960 to 2013 to test the implications of my theory. I find that the regional diversity of coalitions increases the odds of state amicus curiae filers obtaining their preferred outcome, but the ideological heterogeneity of the group of states does not. This latter result is interesting given that it is contrary to the theoretical expectations of the existing scholarship on state amicus filings.
