Legislative history is the step-by-step process by which a bill becomes law -- from introduction in one of the Houses of Congress to the President's signature (if it gets that far). The documents produced by Congress during this process are used to determine Congressional intent or to clarify vague statutory language. These documents carry only persuasive legal authority.
The most important documents produced during the legislative process, that is the documents most indicative of legislative intent, are as follows:
1. Conference Report (if there is one)
2. Committee Report
3. Committee Hearing Transcript
4. Floor Debates
Always look for these materials first when researching legislative history.