Unanimous consent agreements are special orders of the Senate that are agreed to without objection by the chamber's membership. Fundamental to the management of the contemporary Senate, these devices are typically employed to structure floor proceedings and to expedite the chamber's business. Two general types of unanimous consent permeate Senate operations: "simple" and "complex." Both types set aside the rules, precedents, or orders of the Senate via the unanimous concurrence of all Senators. A simple unanimous consent request addresses routine matters, such as dispensing with quorum calls or requesting that certain staff aides have floor privileges. To be sure, there are occasions when a simple unanimous consent request can have policy consequences, such as an objection to setting aside an amendment or dispensing with the reading of an amendment. Simple unanimous consent requests have been used since the First Congress. For example, a Senate rule adopted on April 16, 1789, stated: Every bill shall receive three readings [prior] to its being passed; and the President [of the Senate] shall give notice at each, whether it be first, second, or third; which readings shall be on three different days, unless the Senate unanimously directs otherwise. The focus of this report is on the complex variety: their historical origin, some benchmarks in their evolution, and how they came to be reflected in the Senate's rulebook. Complex agreements establish a tailor-made procedure for virtually anything taken up by the Senate, such as bills, joint resolutions, concurrent resolutions, simple resolutions, amendments, nominations, treaties, or conference reports. As two Senate parliamentarians wrote: There is a fundamental difference between the Senate operating under a unanimous consent agreement and the Senate operating under the Standing Rules. Whereas the Senate Rules permit virtually unlimited debate, and very few restrictions on the right to offer amendments, these agreements usually limit time for debate and the right of Senators to offer amendments. Senators generally accept the debate and amendment restrictions common to most unanimous consent agreements largely for two overlapping reasons: they facilitate the processing of the Senate's workload, and they serve the interests of individual lawmakers. Based on trust, and reached after often protracted negotiations, unanimous consent agreements are the equivalent of "binding contracts" that can only be changed or modified by unanimous consent. It is not clear when the Senate actually began to employ unanimous consent agreements to limit debate or to fix a time for a vote on a measure. Perhaps the first instance occurred in the mid-1840s. On March 24, 1846, Senator William Allen, D-OH, stated that the Senate had been debating a joint resolution concerning the Oregon Territory for more than two months, and it was now time to proceed to a final vote on the matter. Noting that the Senate neither allowed for the previous question (a motion employed in the House to end debate) nor adopted resolutions directing that a vote should occur at a specific time, Senator Allen pointed out that it was the Senate's habit to have "a conversational understanding that an end would be put to a protracted debate at a particular time." A Senate colleague suggested that Allen delay several days before making such a request. Two days later Senator Allen again asked that the Senate informally agree to fix "a definite day on which the vote might be taken." The Senate, he said, should simply refuse to adjourn until there is a final vote. No action occurred on Allen's recommendation. On April 13, 1846, however, a consensus developed among Senators that a final vote on the joint resolution should occur three days later. Finally, after spending around 65 days debating the matter, the Senate on April 16 enacted the joint resolution. Indeed, if this was the first time that the Senate employed something like a unanimous consent agreement to end debate and precipitate a vote on a measure, there is little question that these accords became both more commonly used and more sophisticated in their procedural features. By 1870, noted two scholars, unanimous consent agreements "were being used with some frequency." These early unanimous consent agreements were, "as they are today, time-limitation agreements that provided for the disposal of a measure by a specified time." An April 24, 1879, exchange illustrates the practical use of these accords for limiting debate and setting the time for a vote. The exchange is reminiscent of what occurs in today's Senate. The President pro tempore . The Chair will once more state the proposition and again ask the Senate whether there be any objection to it. The proposition is, that at three o'clock to-morrow, all debate on this bill shall cease, and the Senate shall then proceed to vote upon the pending amendment or amendments that may be offered, and finally on the bill itself without debate. Mr. Conkling . That is right. The President pro tempore . Is there objection to that understanding. The Chair hears none, and it is agreed to. Bill managers apparently took the initiative in propounding unanimous consent agreements. Their increasing use in subsequent decades led one Senator, Roger Mills, D-TX, to complain that the Senate "reaches its vote on all questions like the historic Diet of Poland, by the unanimous agreement of the whole, and not by the act of the majority." Other issues associated with these early accords also sowed confusion among the membership. Many of the complaints stemmed from the fact that the early unanimous consent agreements were often viewed "as an arrangement simply between gentlemen" and could, as a president pro tempore once said, be "violated with impunity by any member of the Senate." To reduce the confusion, the Senate adopted a new rule. The fundamental objective of Rule XII was to clarify several uncertainties associated with these senatorial contracts. In the early 1900s, the Senate took modest steps to reduce some of the confusion associated with unanimous consent agreements, such as requiring these accords to be submitted in writing to the desk, read to the chamber, and "printed on the title page of the daily calendar of business as long as they were operative." More changes were in the offing, however. Two overlapping factors explain why the Senate agreed to a formal rules change to govern these accords. First, there were a couple of ambiguities associated with these accords that continued to arouse contention and confusion. Past precedents simply did not adequately address these recurring problems. Second, a riveting event—a Senator was caught by "surprise" when a unanimous consent agreement was entered into—underscored the need for a formal rule (Rule XII) to clear up issues associated with these "gentlemen's agreements." On the matter of ambiguity, there were two principal issues. First, could these agreements be changed or modified by another unanimous consent agreement? Second, could the presiding officer enforce these accords? Today, both principles are accepted as procedural "givens." Not so several decades ago. For example, on March 3, 1897, Senator George Hoar, R-MA, stated: "I think it is very serious, indeed, under any circumstances, to set the precedent of revoking a unanimous-consent agreement by other unanimous-consent agreements." As another example, one of the Senate's institutional leaders, Henry Cabot Lodge, R-MA., argued: "If it is to be supposed that unanimous-consent agreements are to be modified, we shall soon find it impossible to get a unanimous-consent agreement. I think nothing is more important than the rigidity with which the Senate preserves unanimous-consent agreements." Or as Senator Joseph O'Gorman, D-NY, stated: "Has it not been established by the precedents of this body that a unanimous-consent agreement could not be impaired or modified either by another unanimous-consent agreement or by an order of the Senate?" To be sure, other Senators contended that these compacts could be modified by another unanimous consent agreement. As to the enforcement of these accords, presiding officers took different positions. As one presiding officer observed, "it has been the universal ruling of the Chair that the Chair can not enforce a unanimous-consent agreement, but that it must rest with the honor of Senators themselves." On another occasion, the president of the Senate asked: "[W]hat is the pleasure of the Senate, whether he shall enforce the agreements entered into by unanimous consent or not?" Senator John Sherman, R-OH, replied that the chair should "enforce the agreement with respect to the bill under consideration." The chair then asked, "In similar cases, what is the pleasure of the Senate?" Senator Eugene Hale, R-ME, provided this answer: "We'll cross that bridge when we reach it." Contrarily, "Vice Presidents Charles Fairbanks and James Sherman were not timid about enforcing [unanimous consent agreements] at times." Sundry other issues were also associated with these compacts. For example, Senators argued about whether a motion to recommit a bill violated a unanimous consent agreement to vote on the bill. Some Senators said that if they were not present when a unanimous consent agreement was proposed, colleagues could object for them. In response, Senator Thomas Martin, VA, the ostensible Democratic floor leader, stated: "When unanimous consent is asked, unless objection is made from the floor of the Senate by a Senator who is present, he can not leave his vote here to be recorded against it. The Senate can not do business by proxy that way." Senator Reed Smoot, R-UT, was caught off-guard when a unanimous consent agreement he opposed was agreed to. The issue involved a 1913 bill (S. 4043) to prohibit interstate commerce in intoxicating liquors. A unanimous consent agreement was properly made and announced by the presiding officer. Senator Smoot, who was present in the chamber, had planned to object but was momentarily distracted and failed to lodge a timely dissent. For the next two days the Senate debated the legitimacy of the unanimous consent agreement and whether it could be modified by another unanimous consent agreement.