In introducing this special issue of Comparative American Studies, this essay traces a history of attempts to define and practice a transnational American studies, and suggests that such efforts face inherent and perhaps intractable difficulties. It then explains this issue's rationale for approaching the culture, literature, and history of California through a transnational lens, proposing why we might productively, indeed necessarily, think of this subnational entity as a transnational one. It does so by discussing and responding to the different ways in which a transnational conception of California is constructed and mobilised in each of this issue's constituent articles.