What are the constitutional norms for self-interpretation – that is, the constitutional rules governing whether and when a government body has the power to issue controlling interpretations of legal texts that it drafted? The answer to this question could determine the fate of Seminole Rock deference, the nearly seventy-year-old doctrine enabling agencies to issue controlling interpretations of their own regulations. Jurists and scholars have argued that the doctrine runs afoul of a constitutional norm against self-interpretation, and last term Chief Justice Roberts asked future litigants to brief whether the court should overturn the doctrine on this basis. This Article is the first to comprehensively examine constitutional self-interpretation norms by looking at the conditions under which the heads of the three branches of government exercise self-interpretation powers. It shows that self-interpretation is pervasive and that the Supreme Court would be wrong to overturn Seminole Rock on self-interpretation grounds. Moreover, by examining self-interpretation practices, this Article brings new insight to the many areas of law that involve self-interpretation, including presidential oversight of agencies and judicial stare decisis.