Abstract: There is a principle of constitutional law holding that "one legislature may not bind the legislative authority of its successors." The Supreme Court recently discussed that principle at length in United States v. Winstar, and although the case was decided on other grounds, it is clear that the Court sees the principle as a constitutional axiom. When cashed out in terms of constitutional doctrine, the principle means that legislatures may not enact entrenching statutes or entrenching rules: statutes or rules that bind the exercise of legislative power, by a subsequent legislature, over the subject matter of the entrenching provision. Judges have applied this rule of constitutional law in various settings, and the academic literature takes the rule as given, universally assuming that legislative entrenchment is constitutionally or normatively objectionable. The goal of the academic literature has been to supply the definitive rationale for the rule, although the theorists' favorite rationales are all different. Our claim is that the rule barring legislative entrenchment should be discarded; legislatures should be allowed to bind their successors, subject to any independent constitutional limits in force. The rule has no deep justification in constitutional text and structure, political norms of representation and deliberation, efficiency, or any other source. There just is no rationale to be found; the academics have been on a fruitless quest. Entrenchment is no more objectionable in terms of constitutional, political, or economic theory than are sunset clauses, conditional legislation and delegation, the creation, modification, and abolition of administrative agencies, or any of the myriad of other policy instruments that legislatures use to shape the legal and institutional environment of future legislation. In Part I, we define our terms, rebut the view that entrenchment is conceptually impossible, and argue that entrenchment is both constitutionally permissible and, in appropriate circumstances, normatively attractive. In Part II, we apply our analysis to a wide range of entrenchment-related problems, including the validity of the Senate cloture rules, the Gramm-Rudman law, legislatively enacted canons of statutory interpretation, statutes that regulate internal congressional procedures, government contracts, treaties, and entrenchment within the executive and judicial branches. Part III is a brief conclusion.