Abstract: The federal constitution contains a set of rules that I will describe as the constitutional law of congressional procedure. These are rules that regulate the internal decisionmaking procedures of Congress; absent specific constitutional provision, they would be subject to the authority of each House to "determine the Rules of its Proceedings." The constitutional law of congressional procedure encompasses the long catalogue of provisions in Article I, Section 4-5, which includes rules for assembling the legislature, selecting its officers, and disciplining its members; voting and quorum rules; rules governing the transparency of deliberation and voting; and a range of other provisions. It also encompasses other important rules scattered elsewhere in Articles I and II, such as the Origination Clause, special quorum rules for supermajority voting, and the special procedures for overriding a presidential veto. The constitutional law of congressional procedure has rarely been analyzed as an integrated body of rules, largely because of historical quirks in the relevant sectors of political science and constitutional law. The article's project is to examine this body of rules as a unified topic that is central to the constitutional design of legislative power. The project is instrumental and prescriptive; the article asks how the Constitution's rules of congressional procedure might be structured to advance a congeries of widely-shared aims. The relevant rules should, among other things, promote congressional deliberation that is well-informed and cognitively undistorted, minimize the principal-agent problems inherent in legislative representation, and encourage technically efficient use of constrained legislative resources, especially time. The difficult enterprise is not stating the aims to which well-designed legislative procedure should conduce, but rather negotiating the inevitable tradeoffs between and among them. Part I surveys the methodological problems that constitutional framers designing legislative procedure must confront, especially the key problem whether and when rules of legislative procedure should be promulgated in the Constitution itself, or instead be committed to the discretion of future congresses through a general grant of rulemaking power. Part II considers in turn the timing of congressional sessions, the admission and expulsion of legislators, the selection of legislative officers, voting and quorum rules, the transparency of legislative deliberation and voting, the rule barring the Senate from originating revenue bills, and the question whether Congress may enact binding statutes that prescribe internal rules for the two Houses taken separately. This Part also considers rules of legislative procedure that appear in state and foreign constitutions, and whose absence from our own itself poses interesting puzzles. Examples are rules requiring three readings before a bill may be enacted, and rules that bar the introduction or enactment of bills at the close of the legislative session. Throughout Part II, the aim is to identify design defects, to evaluate alternatives and innovations found in state and foreign constitutions, and to propose interpretive choices or constitutional reforms that might improve the constitutional law of congressional procedure.