Abstract: Legal and political theory have paid a great deal of attention to supermajority rules, which require a fraction of votes greater than 1/2+1 to reach a decision, and thus empower a minority to block change. In this paper I consider the opposite deviation from simple majority rule: submajority rules, under which a voting minority is granted the affirmative power to change the status quo. Among the examples I will consider are: - The Journal Clause, which allows 1/5 of the legislators present in either House to force a roll-call vote; - The discharge rule in the House, which (at various points, although not today) has permitted a specified minority of legislators to force bills out of committee for consideration on the floor; - Senate Rule XXII, under which a cloture petition is valid when signed by sixteen Senators; - The Seven Member Rule, under which a minority of designated committees in the House and Senate can require the executive branch to divulge information; - House Rule XI, which entitles committee minorities to call witnesses at hearings; - The famous Rule of Four that allows four Justices to grant a writ of certiorari and thereby put a case on the Supreme Court's agenda; - Rules governing direct democracy that permit a defined minority of a state's electorate to place a question on the ballot, or to force a recall election; - Rules governing international organizations, which frequently allow a defined minority to call an emergency session or to force a roll-call vote. Submajority rules are rarely discussed, either because they are assumed not to exist, or because they are assumed to lack any institutional virtues, or because submajoritarian decisions are assumed to be chronically unstable in light of the risk that subsequent majorities will reverse the submajority's decision. I will dispute all three assumptions. Submajority rules have important procedural and deliberative virtues: in a range of situations they enable a minority to force public accountability upon a majority, to the benefit of the institution as a whole. The reversibility problem can be, and is, dampened by other institutional rules and norms that protect submajoritarian decisions, or by the simpler expedient of adopting submajority rules only for decisions that are inherently irreversible or costly to reverse, such as decisions that release information into the public domain.