Any given provision in the current United States Code (“U.S. Code”) may be the product of multiple acts passed over a long period of time. So, how do you unpack the provision and discover the different acts that gave rise to a particular section of the U.S. Code? Tracing legislation from the U.S. Code back to the bills, public laws, and Statutes at Large may seem daunting for the uninitiated, but we hope this section will help simplify the process.
The first step in tracing a piece of legislation will be to look at the U.S. Code section of interest in a print or online resource. For more information about where to find the U.S. Code in print and online, we suggest reviewing our companion research guide, Federal Statutes: A Beginner’s Guide, particularly the page on the United States Code.
To determine which law created your U.S. Code section, and which law or laws may have amended the section over the years, you will want to look to the very end of the U.S. Code section for a series of citations enclosed in parentheses. This group of citations is called a “source credit” or “source note,” and it lists all of the laws that have affected or created your U.S. Code section. Each source credit will be laid out chronologically, with the first citation giving information about the public law that gave rise to the U.S. Code section, and each subsequent citation (separated by a semicolon) providing information about the public laws that amended the U.S. Code section.
We want to be sure to note that, if you choose to use a free online resource for tracing purposes, there might not always be source credit information available. As such, we suggest using the online United States Code provided by the Office of the Law Revision Counsel of the U.S. House of Representatives (OLRC), the organization that publishes the official U.S. Code. This website not only provides source notes, but even provides a link to the source note at the top of each U.S. Code section. In addition to the source note, the ORLC website provides an “Amendments” note after each U.S. Code section that will typically list how each subsection of the U.S. Code section was changed by each amending public law (organized by year of the amendment).
After finding the source credit, you will see that each citation listed has at least three pieces of information—a public law number or chapter number, the date the public law was enacted, and a citation to where the public law can be found in the United States Statutes at Large. The United States Statutes at Large citation lists a number, then the abbreviation “Stat.” and then another number—the first number is the volume number, and the second number is the page on which the pertinent section of the public law begins (example: 46 Stat. 142).
As specified in Federal Statutes: A Beginner’s Guide, free online access to the United States Statutes at Large is determined by when the public law was passed. For public laws passed before 1951, you can visit A Century of Lawmaking for a New Nation (1789-1875, in TIFF format) or the Law Library's digitized Statutes at Large collection (1789-1950, in PDF format by volume). To find public laws passed from 1951 to the present, you can use Congress.gov or GovInfo. On GovInfo, navigate to the category Bills and Statutes and then select either Statutes at Large (1951 to present) or Public and Private Laws (1995 to present).
Finding the public laws in the United States Statutes at Large might be the end of the research trail for those interested in how a law has changed over time. However, many researchers are also interested in the legislative history documents (such as congressional committee hearings and reports, congressional debates, etc.) attached to the bills and resolutions that eventually became these public laws. To find the pertinent bill numbers for public laws from 1904 to the present, simply look to the first page of the public law as it is printed in the United States Statutes at Large. To the immediate left or right (depending on whether the public law starts on an even or odd page) of the first section of the public law, there will be information about both the bill number and date of enactment.
 Note that, if the U.S. Code title is a positive law title, there may also be “Historical and Revision Notes,” which “specify the laws that formed the basis of sections that were included in the title when the title was first enacted into positive law. The first act in the source credits for such a section is the act that enacted the title into positive law.”
 To find the bill numbers related to public laws passed before 1904, we suggest using Eugene Nabors’ Legislative Reference Checklist: The Key To Legislative Histories From 1789 To 1903.