"Legislative history" refers to the background and events leading to the enactment of a statute, including hearings, committee reports, and floor debates. Legislative history can be used to aid in interpreting the statute (Black's Law Dictionary).
A Bill is Introduced in Congress
The federal legislative process typically begins with introduction of a bill in the House of Representatives or the Senate. Bills are numbered sequentially as they are introduced. The bill may be referred to a congressional committee responsible for the bill's subject matter for consideration. Bills die at the end of the two-year Congress in which they are introduced if not enacted.
Committee Hearings, Reports & Prints
Congressional hearings gather facts, data, and expert opinions on the subject of the bill. The committee may amend a bill referred to it in a markup session. The committee issues a report discussing its deliberations when it votes favorably on a bill. Committee reports are considered to be the most significant parts of a legislative history because they discuss Congress's intent in passing the bill. Transcripts of hearings, prepared testimony by hearing witnesses, and supporting documents (committee prints) also become part of the bill's legislative history.
Floor Action & Debate
Bills reported favorably out of committee are brought up for floor action by the full House or Senate. There the bill may be debated and amended before being passed by that chamber. Once passed by one chamber of Congress, the "engrossed" bill is printed in the Congressional Record and referred to the other chamber of Congress.
Conference Committee Reports
The engrossed bill goes through the same process in the other chamber. The bill may be passed by the second chamber in substantially the same version as it was received, or it may be further amended; in that case a conference committee must be convened to agree on a final version.
The conference committee is made of up of members of both houses of Congress. If they agree on a reconciled version of a bill, they issue a conference report containing the agreed language and an explanation of their deliberations, which is printed in the Congressional Record. The conference report and amended bill must be debated by both the House of Representatives and Senate and passed without further change by both. The final version of the bill is known as an "enrolled" bill.
The enrolled bill is sent to the President for signature. The President must sign the bill within ten days for the bill to become law, or may veto the bill and send it back to Congress with a veto message (a Summary of Bills Vetoed from 1789 - present is on the U.S. Senate website). An overrideof a presidential veto requires two-thirds of all members of Congress to vote to override. If the President takes no action on a bill sent to him within ten days, it becomes law even without his signature if Congress is still in session; however, if Congress has adjourned, the President's lack of action is known as a pocket veto and the bill fails to become a law. When the President signs a bill, it is immediately effective as law; a signing statement may also accompany it. It is assigned a Public Law number and published as a "slip law."
Congressional documents are also part of legislative history research. These documents are not prepared in Congress; they may include reports of administrative agencies, presidential messages, reports of special investigations made for Congress, and submissions by non-governmental organizations and interested citizens. There are four types of congressional documents: House and Senate Documents; Senate Executive Documents; and Senate Treaty Documents.
The legislative process followed by most state legislatures is roughly the same as that in Congress.