While international law has existed for several centuries, State responsibility — the remedial rules triggered when a State breaches international law — is a modern phenomenon. Its creation resulted from two nineteenth century events: the U.S. protection of foreign investments and the German doctrinalization of public law. I will argue that contemporary doctrines of State responsibility are institutional reactions to and continuations of these separate developments. As a result, the same norms do not apply to all international disputes. For example, the rules the International Court of Justice employed to hold Serbia responsible for the Srebrenica massacre do not resemble those that the NAFTA arbitration panel used to hold Mexico responsible for expropriating an American corporation’s property. In the aftermath of the First World War, the League of Nations sought to codify State responsibility based on intra-American arbitrations; however, this effort failed because Latin American countries viewed that practice as imperialistic. Later attempts succeeded when the U.N. dissociated codification from the practice and relied instead on abstract German theory. As I will explain below, the successful codification of State responsibility had little effect on the American practice of investor protection. Accordingly, I describe international law enforcement in terms of two separate doctrines: one “spoken” and the other “unspoken.” International organizations such as the International Court of Justice regularly invoke the codified principles of State responsibility. At the same time, the American manner of investment protection has become the mainstay of international dispute resolution — though it remains unarticulated. Given the centrality of State responsibility to international law enforcement, its codification provides an opportunity to consider the relationship between doctrine and practice. Because the U.N. divorced the codification of State responsibility from international practice, it formulated a global rule of law and, simultaneously, provided the means for bypassing the very structure it created. As a result, there remain two frameworks of international law enforcement: the institutional, which is practiced by the “pure” international lawyers, and the ad hoc, which continues to be conducted by the “commercial” international lawyers. As long as international institutions continue to ritualistically affirm the U.N. doctrine, the controversial American practice of investment protection will continue unabated.