The official United States Code is compiled by the Office of the Law Revision Counsel (OLRC) and published every six years, with annual updates. The GPO sells unannotated print editions of the official Code, but most people use the annotated editions or the free Internet editions, discussed below.
Free Internet Editions: The official electronic edition of the USC is prepared and posted free by the Office of the Law Revision Counsel (OLRC) of the U.S. House of Representatives. The OLRC also posts the Code in .PDF format.
Other free editions with additional features are posted by Cornell University's Legal Information Institute, FindLaw and the GPO's FDsys. Note that these electronic editions are not current, but the Web sites all provide ways of locating the new legislation that affects each section. I think the Legal Information Institute site makes it relatively easy to identify updates.
If you have access through a state bar association, Casemaker and Fastcase provide more current editions with good searching.
Annotated Editions: The annotated editions of the U.S. Code are: the United States Code Annotated (USCA), by Thomson/West; and the United States Code Service (USCS) by LexisNexis. Both sets are excellent.
There are a few important differences between the two annotated Codes, including the following. The USCS follows Statutes at Large, while the USCA follows the official USC. The USCS has a cross-reference table to the CFR; the USCA doesn't. The USCS includes more cases but the USCA has more annotations per case. The USCS is updated and invoiced monthly, while the USCA is updated and invoiced annually.
The USCA is available on Westlaw (USCA), while the USCS is on Lexis (GENFED;USCS). For more information, see "Fee-based Databases," below.
For more about the different print versions of the USC, see Using the United States Code.
Fee-Based Databases: Unannotated versions of the USC are available on Lexis (GENFED;USC), Westlaw (USC), Bloomberg Law, LOIS, Fastcase and Versuslaw.
The annotated USCS is on Lexis (GENFED;USCS), and the annotated USCA is on Westlaw (USCA). The appropriate format for pulling a section on Lexis is: x uscs x. The format on Westlaw is: x usca x.
Lexis and Westlaw update their online code as new laws are passed; still, there is about a two-month time lag when Congress is in session. Running a Shepard's or KeyCite report on the relevant section will tell bring you within 10 days of currency. To get even more current, search the bill number of any pending legislation that shows up on the Shepard's or KeyCite report in a Congressional Record database -- e.g., on Westlaw, use the CR database and search with the format: "(HR /10 235 767 1438) & da(after 12/10/200x)".
The unannotated versions of the code on CQ Roll Call and Bloomberg Law (both available only by subscription) are updated within a month or so of the date new legislation takes effect.
Additional sources for the U.S. Code are discussed in the LLSDC's Legislative Sourcebook; scroll down to the link called "Electronic Sources for U.S. Statutes and the U.S. Code."
Historical Editions: Historical editions of the unannotated USC are posted free back to 1988 by the Office of Law Review Commission and back to 1994 on FDsys. Westlaw offers historical editions of the USCA back to 1990 (USCAxx, with the "xx" being the last two digits of the relevant year). Lexis offers historical editions of the USCS back to 1992. HeinOnline subscribers can get historical editions back to the 1925-1926 edition. Bloomberg Law goes back to 1994.
Alternatively, and for older editions of the Code, many large academic and government law libraries keep old sets of the U.S. Code. I know that the New York County Lawyers' Association library has historical editions of the U.S. Code, at least back to the early part of the century, and maybe earlier. You can call in a request (212-267-6646, x204,-5,-6 or -7), and they will copy sections and fax. You could also call the Law Revision Counsel at the House of Representatives (202-226-2411). The University of Baltimore law library has historical editions of the unannotated, official United States Code, which is published every four years (410-837-4570 phone; fax requests to 410-837-4570).
Pending Legislation: House and Senate bills generally state exactly where they would change the text of the U.S. Code, although seeing the impact can be difficult. To make this easier, CQ Roll Call and Potomac Publishing each offer "Legislative Impact" databases that display the relevant Code sections as they would be affected by pending bills.
To identify pending and/or recently enacted legislation that could affect a Code section, run a Shepard's or KeyCite report on the section.
Public Laws: The citation for the Public Law(s) that created and/or amended each section of the Code are listed in the annotations after the section in the USCA or USCS. For information on how to get the full text of a Public Law, see "Public Laws."
If you have a Public Law number and you want to see where it has been put into the U.S.C., use the sources listed in the separate entry for "Public Laws."
For a discussion of Federal legislation and the USC, see Fundamentals of Legal Research (West).
Missing Sections: If you have a citation for a section that seems to be "missing," check the "Revised Titles" section at the end of the USCS to see if it has been renumbered. Also, remember that the Code contains only law that are permanent (not temporary) and of general impact (not specific, such as naming a post office). And some laws are inserted into the Code as Notes or Appendices (discussed below). For more information, see Will Tress' "Lost Laws: What We Can't Find in the United States Code," 40 Golden Gate U. L. Rev. 129 (2009-2010).
Notes and Appendices: The Office of Law Revision Council (OLRC) puts several kinds of "Notes" at the end of some Code sections. If a Congress doesn't specify where a Public Law should go in the Code, the Office sometimes puts it into a Note at the end of a related code section (or into an Appendix at the end of a title). You would officially reference this text by the Public Law number, but unofficially you could use the format: xx USC xxxx note. To see if the law was repealed, look in a current edition of the Code or check "Table III - Statute at Large" (available on the United States Statutes and the United States Code page of the LLSDC Legislative Sourcebook. Laws codified in Notes and Appendices are have the same legal force as laws codified in their own Code sections, see The Authority of Statutes Placed in Section Notes of the United States Code by Rick McKinney.
The OLRC also adds editorial notes to explain the codification, to note errors in an enacted law, to explain an amendment or to clarify the effective date of the section. The notes also list the Public Laws enacting and amending the related code section and provide and may cross reference other Code sections or related executive orders.
Popular Names: Many statutes have "Short Titles" or "Popular Names" (e.g., the "Hart-Scott-Rodono Act"), and you can look up where they are codified using a "Popular Name Table." Popular name tables are posted by the Office of the Law Revision Counsel and the Legal Information Institute. You can also find a Popular Name Table at the end of the United States Code Annotated and the United States Code Service, available in print and online through Westlaw (USCA-POP) and Lexis, respectively (click here for information about searching the PNT on Lexis).
Predecessor Publications: The Revised Statutes of 1873 and 1878. The U.S. Code has a predecessor publication called the "Revised Statutes." The original Revised Statutes was introduced in the House of Representatives in 1873, enacted in 1874 and published in 1875. It is known as the "Revised Statutes of 1873, though the official title is the Revised Statutes Passed at the 1st Session of 43d Congress, 1873-1874, Embracing Statutes, General and Permanent in Nature, in Force December 1, 1873). It was published as Part I of Volume 18 of Statutes At Large.
The Revised Statutes of 1873 was soon corrected and amended and re-published as the Revised Statutes of 1878. I read that the government published a replacement Volume 18 of Statutes At Large when the Revised Statutes of 18 came out.
You can find a clunky scanned edition of the Revised Statutes of 1873 posted free at the bottom of the Statutes at Large, 1789-1875 page of the Library of Congress' American Memory collection. More usable editions of the Revised Statutes of both 1873 and 1878 are available on HeinOnline. Some academic and large government libraries still have the print.
In 1926, Congress published the Code of Laws of the United States of America of a General and Permanent Nature in Force December 7, 1925, which is now known as the first edition of the United States Code.