The Code of Federal Regulations is a publication established by Act of Congress (44 U.S.C. § 1510). It represents a compilation of all the regulations issued by Federal administrative agencies that have "general applicability and legal effect." As a consequence the contents of the CFR covers a wide range of subjects. Most states prepare comparable compilations of state agency regulations, generally called their "Administrative Code." [State Administrative Codes]
Federal statutes furnish the authority and the limits for regulations that appear in the CFR. This means that the regulations on a subject should be read together with any pertinent portions of the U.S. Code. [U.S. Code] It also means that courts will, upon occasion, hold that regulations which appear in the Code of Federal Regulations are invalid because they conflict with a Federal statute.
The regulations appearing in the CFR may be incomplete or even obsolete because of amendments issued after the date the particular title was last revised. This makes it important to note the revision date of the portion of the CFR you are using and, when being sure you have the up-to-date regulations is critical, checking for amendments.
Amendments appear, as they are issued by the government, in the Federal Register which is also available in searchable form at the U.S. Government Printing Office site. This is not only true of new regulations in their final form but also proposed changes. [Federal Register Search] The GPO site provides guidance on how to search for material in the Federal Register affecting particular parts of the CFR. [Guidance]