Bills are proposed laws introduced in Congress but not yet enacted. Laws have been passed by both houses of Congress and signed by the President. Tracing the bill history of an enacted law can be helpful in determining the legislative intent behind the law, which can help in its interpretation. After the laws are passed, they're cumulated into Statutes at Large for a whole Congress. Then, the "gist" of the law is summarized by subject in the U.S. Code. Here's a graphical representation of this journey:
Laws are usually cited by their Public Law (PL) number, but you may see a citation by their place in the Statutes at Large. The Statutes are a cumulation of laws from a particular Congress. Looking at the "Lilly Ledbetter Fair Pay Act," passed in the 111th Congress:
(NOTE: There are also Private Laws, passed for the relief, or on behalf of, individuals, and only have application in the individual cases.)
Sections of the U.S. Code are cited by title (which is like a chapter) and section. For example, the section of the Code dealing with military promotions begins with Section 619 of Title 10. It would be cited: 10 USC 619.
Code of Federal Regulations
Federal Register. This is the official daily publication for rules, proposed rules, and notices of Federal agencies and organizations, as well as executive orders and other presidential documents. It is updated daily by 6 a.m. and is published Monday through Friday, except Federal holidays. Proposed Regulations must first appear in the Federal Register which is available online at through govinfo.gov.
Citations to the Federal Register follow this form: [volume no.] FR [page no.].
Code of Federal Regulations (CFR). The annual edition of the CFR is the codification of the general and permanent rules published in the Federal Register by the departments and agencies of the Federal Government. It is divided into 50 titles that represent broad areas subject to Federal regulation. The titles are updated once each calendar year, on a staggered basis. Once the Regulations are in force, they appear in the CFR in summary form.The annual editions are online through govinfo.gov.
Citations to the CFR look like this: [title no.] CFR [section no.]. For example, the section of the CFR that deals with launch licenses for commercial space transportation is section 415 of title 14, so the citation would be 14 CFR 415.
The Law Library keeps complete microfiche backfiles for both the Federal Register and the CFR. Note that the Federal Register began publication in 1936 and the CFR in 1937.
The Blume Library has a print copy of the latest index to the CFR, in the Documents Collection at AE 2.106/3-2: .
Several commercial products are designed to keep people in business, and other fields, abreast of new developments which may affect their work. The Law Library subscribes to many of these services in different areas. Ask a Law Librarian for assistance.
The Constitution, ratified in 1789, is the root and backbone of all of our laws. Given its importance, it's really a pretty simple document. You can read a transcript, see images of the original (from which the graphic below was taken), and learn about the history of the document at the National Archives website.
Here are some other sources of the Constitution, as well as analysis and annotated references to relevant cases:
Congress.gov is the go-to site for Congressional information past and present.
The new site has great new features and more content. Generally speaking, Congress.gov is set up for efficient browsing if you don't have the exact information (a bill number, for example) that you need. Just limit using their wide variety of facets to whittle your search results down.