To argue, as this contribution does, that European integration enjoys an “administrative, not constitutional” legitimacy is to take a position in obvious tension with the deeply-rooted conceptual framework—what we might call the “constitutional, not international” perspective—that has dominated European public-law scholarship over many decades. Rather than viewing the administrative alternative as an outright rejection of all that has come before it, however, one can in fact see it as providing the legal-historical micro-foundations for certain better-known theories of European legal integration. I am referring in particular to Joseph Weiler’s classic theory of European “equilibrium” (now updated as “constitutional tolerance”), as well as Kalypso Nicolaϊdis’s more recently developed “demoi-cratic” theory of European governance (on which this contribution focuses in particular). The central idea behind the administrative interpretation—the historical-constructivist understanding of “delegation” and the essential balance it demands between supranational regulatory power and national democratic and constitutional legitimacy—directly complements both theories. This alternative interpretation suggests how the balance between the national and supranational, as well as the nationally mediated legitimacy that is essential to integration’s sustainability, in fact have their origins in the historical evolution of administrative governance over the course of the twentieth century. Integration’s grounding in the history of administrative governance helps to explain certain crucial but often overlooked aspects of European public law, most importantly the role of oversight by national constitutional bodies—executive, legislative, and judicial—in the legitimation of the integration process. Moreover, the administrative perspective also provides helpful insight into how the theories of European “equilibrium” and “demoi-cracy” might be legally operationalized in service further European reform, particularly in the context of the still-unresolved Eurozone crisis.