The bill, co-authored by Senators Richard Lugar (Republican, Indiana), chairman of the Senate Foreign Relations Committee and Joe Biden (Democrat, Delaware), ranking Democrat on the committee, was earlier passed by the Senate Foreign Relations Committee June 29 by a margin of 16-2.

This first step, taken after the Committee extensively considers a bill, 'enables' the legislation -- meaning it sends the bill to the full Senate for debate and voting.

The first step in this process is for the bill to be placed on the Legislative Calendar -- a function of outgoing Majority Leader Bill Frist (Republican, Tennessee). It was due to be brought before the Senate last month, but a disagreement between the Democrats and Republicans prevented that event.

While it is Senator Frist's prerogative to place a bill on the calendar, legislation can be brought to the floor whenever a majority of the Senate choses -- in other words, when the bill is called, the majority of Senators present can decide to consider the bill, or to postpone such consideration.

This vote is essential before a bill is actually taken up for floor debate.

Once the bill is taken up for consideration, it signals debate on the floor. While debate on the floor of the US House of Representatives is limited by criteria formulated by the House Rules Committee, debate in the Senate is theoretically unlimited. Senators can speak for as long as they like, pro or con -- there are no limitations on the time each individual Senator is allowed.

The Senate differs procedurally from the House in one other important respect: While the House does not permit individual Congressmen to attach riders (amendments or provisions that are not relevant to the legislation where it is attached) to the bill being debated on, Senators face no such restrictions.

Thus, a Senator can attach any rider (s)he likes to any bill, even if said rider is not relevant to the bill in question. Senators can also attach an entire bill as amendment to the one being considered.

The unlimited nature of Senate debate gives individual Senators opposed to a particular piece of legislation a powerful weapon to defeat a bill -- the filibuster.

Common perception of the filibuster is of one Senator speaking endlessly, on any and every subject under the sun, and refusing to yield the floor until the legislation is crippled.

To accomplish this is not easy: while there are no limits to how long a Senator may speak or what subject he may chose to speak on, the filibuster is in effect only so long as the Senator holds the floor continuously. He may not pause for refreshments or for washroom breaks; if he stops speaking for any reason, he may not continue the filibuster.

Endless speeches are not, however, the only filibustering weapon -- the Senator in question can employ a range of parliamentary procedures to accomplish the same end.

For instance, a Senator or Senators can add unlimited amounts of amendments to a bill, relevant or no, and insist that each amendment be fully debated.

Further, he can ask for a constant quorum call to be in effect, thus keeping his fellow Senators there at all hours.

The existing record for filibustering was set in 1957 by the late Senator Strom Thurmond, who spoke for 24 hours and 18 minutes straight to try and block passage of the Civil Rights Act of 1957; in the end, his effort was unsuccessful and the bill ultimately passed.

There are two possible ways around the filibuster. The first is the Unanimous Consent Agreement, by which all Senators agree, before taking up a bill, to limit debate to a specified time frame. If such an agreement is in place, a filibuster cannot be employed.

The other weapon against a filibuster is cloture -- a motion that can be invoked to end a filibuster. For this to take effect, three-fifths of the Senate, or 60 Senators, have to vote in favor. Once cloture is successfully invoked, further debate is capped at 30 hours from that point of time, at the end of which the bill has to be voted on.

One other delaying tactic is the motion to recommit, where a Senator moves that the bill be sent back to the appropriate committee, in this case the Senate Foreign Relations Committee, for further consideration. For such a motion to take effect, a majority of Senators present and voting have to vote in favour.

Once a bill surmounts all these hurdles, it is taken up for vote, and it passes by a simple majority.

If the House and Senate passes the same bill, it goes to the President for approval. If -- as is the case with the India-US nuclear bill -- the House and Senate have passed different bills, it then goes to conference.

Members from each house of the American parliament form a conference committee, to meet and reconcile the two bills, iron out differences, and present one unified bill. The committee is composed of senior members appointed by the presiding officers of the committee that enabled the legislation in the first place -- in this case, Senators Lugar and Biden of the Senate Foreign Relations Committee.

Once the conference committee agrees on a joint bill, it prepares a report that is submitted to both the House and the Senate for approval.

The bill becomes law when a. the President signs it or b. the President does not sign the bill for ten days after it is submitted, and the Senate remains in session during this period.

If the President vetoes the bill, it goes back to Congress. In such a case, the chamber that originated the legislation can override the veto by a vote of two-thirds of those present.

The India-US nuclear bill, however, did not originate in any one chamber -- the House and Senate each had its own version; the bill the President considers was derived in committee.

Hence, in the event of a Presidential veto, both the House and Senate have to override by a vote of two-thirds each.

External links: Full text of Senate legislation S.3709 | Full text of House Resolution 4974