Enrollment
From the Congressional Research Service:An enrolled bill is the final version of a measure agreed to by both chambers. Enrolled bills are printed on parchment and then signed first by the Speaker of the House and secondly by the President of the Senate, or the formally designated Senate presiding officer. Preparing and signing enrolled bills may take significant time, especially at the end of a Congress when many such bills must be prepared. The Speaker and the Senate presiding officer must sign enrolled bills while their respective chambers are in session, unless permission has been granted in advance for them to sign during recesses or adjournments. Sometimes air couriers deliver enrolled bills to these officials when they are away from the capital. A formally designated Speaker pro tempore may sign enrolled bills in the Speaker’s absence; the Senate President pro tempore may designate in writing another Senator to sign enrolled bills in his or her absence. When the officials from both chambers have signed an enrolled bill, the measure is sent the President. There is no deadline within which Congress must submit an enrolled bill to the President. Both houses must pass a concurrent resolution to recall an incorrectly enrolled bill already sent to the President, or to make changes in the text of an enrolled bill still in the possession of the Congress.
History:The Constitution (Article 1, Section 7, Clause 3) lays out a specific legislative process whereby measures become laws:
Every Order, Resolution, or Vote to which the Concurrence of the Senate and House of Representatives may be necessary (except on a question of Adjournment) shall be presented to the President of the United States;
firstly requires that bills being sent – presented – to the President for approval must be identical as passed by both Houses. This emanates from the Great Compromise of the Constitutional Convention of 1787.
James Madison's Virginia Plan envisioned a dominate bicameral – two house – legislature with the lower house (House of Representatives) being elected proportionately by the people and the upper house (Senate) being elected by the lower house. This frightened the smaller states with less population as they feared a tyranny of the majority with little protection for minority rights. It was a very real concern and almost caused the disbandment of the Constitutional Convention. William Patterson of New Jersey (a small state) remarked that "He had rather submit to a monarch, to a despot, than to such a fate. He would not only oppose the plan here but on his return home do every thing in his power to defeat it there." He later submitted the New Jersey Plan for equal representation by State.
Roger Sherman of Connecticut proposed what would become the Great Compromise. This issue of proportional representation by population versus equal representation by state dominated the convention and hotly debated for six weeks from June 9th to July 23rd when it was decided that the House of Representatives would be elected directly and proportionately by the people and the Senate by the state legislatures with equal representation of two senators per state.