Congress relies on two formal means of resolving differences on House and Senate versions of legislation: conference committees and amendments between the houses. Conference committees can be created by the House and Senate after each chamber has disagreed to the position of the other. The House and Senate presiding officers then each appoint conferees, largely drawn from the committees with jurisdiction over the bill, to represent the chamber in conference committee negotiations. Conference committees develop and present compromise legislation, in the form of a conference report, for approval in each chamber. Historically, conference committees have been used to resolve differences on major bills, where policy issues are complex and differences between the chambers are likely to be greater. The process of exchanging amendments between the houses is more often used when differences between the chambers are comparatively small, although sometimes the chambers use it to resolve their differences on major legislation as well. In recent Congresses, the use of conference committees to resolve differences has decreased. Regardless of the formal parliamentary mechanism chosen, in the contemporary Congress the chambers generally arrive at a resolution of the substantive differences between House and Senate versions of a measure through informal, bicameral discussions that might resemble conference committee negotiations even though neither house has officially appointed conferees to consult over a bill. Once the interested legislators have negotiated an acceptable compromise through these discussions, the compromise can then be embodied in an amendment between the houses or, if conferees have been formally appointed, in a conference report. The difference between amendments between the houses and a conference committee is not necessarily in the way a policy compromise is reached but in the formal parliamentary steps taken after the principal negotiators have agreed to a compromise. The purpose of this report is to explain the procedural options for resolving differences through amendments between the houses, and to discuss the procedural effects of resolving differences through this process as an alternative to a conference committee. Throughout the report, the phrase "amendment exchange" is sometimes used as an alternative to the longer but formal name of "amendments between the houses." The report is arranged to identify legislative options at each stage of the amendment exchange process, first for the Senate and then for the House. For each chamber, key procedural differences between amendments between the houses and conference committee are also discussed and then listed in Table 1 (Senate) and Table 2 (House). The answers to frequently asked questions are highlighted throughout the report in separate, shaded text boxes. The final section of the report describes a particularly complicated case of amendment exchange from the 110 th Congress to illustrate a variety of actions the chambers might take. The House and Senate must agree to the same legislative language in the same legislative vehicle before the bill can be presented to the President. The same legislative vehicle means the same numbered bill or resolution; lawmaking measures that originate in the Senate carry the designation S. (bill) or S.J.Res. (joint resolution); measures that originate in the House are designated H.R. (bill) or H.J.Res. (joint resolution). Only one legislative vehicle, with either a Senate or House designation, is sent to the President. After one chamber passes a bill, it sends it to the other chamber. The receiving chamber then typically refers the measure to committee in the same way that measures introduced in that chamber are referred. There is no requirement that one chamber act on a measure approved by the other chamber, and in each Congress many measures are approved only by the originating chamber. In order for a measure to become law, however, the House and Senate must pass the same vehicle with the same text. If one chamber passes a bill and the other chamber agrees to it without amendment, then the legislative process is complete, and the bill is sent to the President. This is extremely common; more than three-quarters of all legislation that became law in recent Congresses passed the second-acting chamber without amendment. Many of these measures that pass this way are salient to relatively few Members of Congress, such as bills naming post offices or other federal buildings. When major legislation is passed without amendment by the second-acting chamber, it usually reflects extensive negotiations between the chambers prior to the passage of the bill in either chamber. In other words, interested Members from the relevant committees and their staff consult beforehand to ensure that the bill that passes the first-acting chamber will be acceptable, without change, to the second-acting chamber. Most major legislation is not passed by the second-acting chamber without amendment, however. In addition, on major policy topics, it is common for both the House and Senate to initiate legislation, such that there is often both a Senate bill (S.___) and a House bill (H.R.___) introduced on a topic. The requirement that the House and Senate act on the same bill with the identical text means that in this situation the House and Senate must (1) select a single measure—either the House or Senate bill—on which they will both act; and (2) agree on the same legislative language. The selection of the measure, or identifying which bill Congress will send to the President, does not restrict either chamber from acting on its preferred legislative language. More specifically, whether the chambers select an "H.R./H.J. Res." or an "S./S.J. Res." as the vehicle on which to resolve differences will not necessarily affect what policy proposals a chamber considers on the floor. Both the House and Senate can amend the legislation sent by the other chamber, and they can amend it in its entirety. The selection of a measure that both chambers will act on is usually straightforward. The bill that passes a chamber first and is sent to the other chamber is normally the bill that is selected as the vehicle and is eventually presented to the President. The Constitution requires, however, that all revenue provisions originate in the House. The House interprets this to include all appropriations measures as well, and the Senate generally defers to the House on this issue because it does not affect the Senate's ability to propose changes to the legislation. For this reason, measures raising revenues or providing for appropriations that are sent to the President will carry a House bill number (H.R. or H.J. Res.). As mentioned above, most of the time, neither chamber finds it advantageous to wait for the other to act before beginning its own work on a major policy initiative. Typically, the committees of jurisdiction from both chambers will consider legislation regardless of what action is taking place on similar topics in the other chamber. At some point, however, the chambers must select one bill to be the vehicle that is sent to the President. The selection of the vehicle is either done at the start of floor consideration or at the very end. It can only be done at the beginning if one of the chambers has already passed a bill on the subject, in which case the other chamber might choose to take up that bill on the floor instead of legislation crafted by its own committee. Usually, in this situation, a full-text substitute amendment, representing the work of the committee of jurisdiction, is presented at the outset of consideration and is effectively treated as the text for further amendment by the chamber. Alternatively, a chamber can take up a bill reported from its own committee. At the conclusion of floor consideration of its own bill, the chamber can take up the companion bill passed by the other chamber, strike all of the text after the enacting clause, and insert the text of the bill it originated. Either way, the chambers have fulfilled the first requirement: selecting the same bill on which to act. The second step, agreeing to the same legislative language, is generally more challenging. If one chamber considers a bill from the other chamber and amends it before passing it, the House and Senate have acted on the same measure, but they have not agreed to the same text. The chambers can resolve their differences over the text either (1) through an amendment exchange, when the chambers shuttle the bill and amendments back and forth between them proposing alternatives in hopes that both houses will eventually agree on the same language; or (2) through a conference committee, a panel of Members from each chamber that meets to resolve the differences between the bill and the amendment(s) proposed by the second-acting chamber. Occasionally, Congress uses both methods to resolve differences on a measure if it first attempts to resolve differences through amendment exchange and then resorts to conference. Although this report discusses some conference committee procedures for comparison purposes, its main subject is the formal parliamentary steps and options associated with an exchange of amendments between the chambers. In both chambers, the procedures applicable to consideration of amendments from the other body change when the chamber reaches what is known as "the stage of disagreement." A chamber enters the stage of disagreement by formally agreeing to a motion or a unanimous consent request that it disagrees to the position of the other chamber, or that it insists on its own position. When both chambers reach the stage of disagreement, they usually form a conference committee. This report almost exclusively addresses the procedures available prior to the stage of disagreement . When the House amends a bill that has already passed the Senate, it sends the bill and its amendment(s) back to the Senate accompanied by a written document that describes what is being transmitted. This document is a message to the Senate, and sometimes the Senate uses the term message to refer to the amendment(s) received from the House. The Senate will generally hold House amendments at the desk for action by the full Senate, rather than refer them to committee. Nothing in Senate rules requires that the Senate consider the House amendments it receives. However, if the Senate wishes to act further on that particular bill or resolution, it must take some action on the House amendments. By long-standing custom, the majority leader usually makes motions and requests affecting the agenda of the Senate, including those concerning House amendments. Under Senate Rule VII, paragraph 3, House amendments are "privileged for consideration" in the Senate, which means that a Senator can request that the Presiding Officer lay the amendments before the Senate.