21 USC Chapter 4, Subchapter III - PREVENTION OF INTRODUCTION AND SPREAD OF CONTAGION

Multiple entries for a section are listed most recent first, within the section.

The Session Year indicates which session of Congress was responsible for the changes classified. The Congress number forms the first part of the Public Law number; each Congress has two sessions.

Abbreviations used in the Description of Change column:

• An empty field implies a standard amendment.
• "new" means a new section or new note, or all new text of an existing section or note.
• "nt" means note.
• "nt [tbl]" means note [table].
• "prec" means preceding.
• "fr" means a transfer from another section.
• "to" means a transfer to another section.
• "omitted" means the section is omitted.
• "repealed" means the section is repealed.
• "nt ed change" and "ed change" - See the Editorial Classification Change Table [pdf].

The Public Law field is linked to the development of the law in the Thomas system at the Library of Congress.

The Statutes at Large field is linked to the text of the law, in the context of its volume of the Statutes at Large, at the Government Printing Office. Please note that it takes a while for these pages to get posted, so for very recent legislation, you need to look at the "enrolled" version at the Thomas site.

The Statutes at Large references have been rendered in the format used as page numbers in the Public Law web pages to which we link, to facilitate copy-paste into browser "find on this (web) page" tools. We are still working on a more direct link facility.

For serious comparison work, we suggest copying all or a portion of the Public Law text into your favorite text editor, for convenient content traversal and window control.

Sections with change type "new" are a special case, still under development. All are now listed, at the title level only.

You will find that occassionally a specific update you notice in a Public Law listed in a classification table will already have made it into the Code. We assume this is an artifact of the LRC edit process. The LII does not edit the LRC content.

Refer to the LRC (Law Revision Council) for explanations about the US Code from the folks who put it all together.

You can look for information about what it is and is not, which titles are positive law, the schedule of Supplements, etc. Under download you can find the source data we use here (GPO locator files), as well as, PDF files that look just like the paper books (these may be rather large).

Refer to the Thomas site for changes that have not yet made it into the classification tables.