Annotated versions of the United States Code are technically unofficial, but add resources after the text of each statute to help researchers determine the relevance of a particular statute and to assist with further research on the topic addressed by that statute.
The Law Library maintains a print copy of both the United States Code Annotated (U.S.C.A.), published by West/Thomson Reuters, and the United States Code Service (U.S.C.S.), published by LexisNexis.
Annotations to individual statutes include historical and statutory notes, references to related federal regulations, recommended secondary sources, and summaries and citations to federal court opinions applying and interpreting the statute (Notes of Decisions in U.S.C.A. and Notes to Decisions in U.S.C.S.).
These annotated versions of the United States Code (U.S.C.) are available online through Westlaw (U.S.C.A.) and Lexis (U.S.C.S.) (See the section on Finding Federal Statutes Using Westlaw & Lexis).
The two annotated versions of the United States Code, U.S.C.A. and U.S.C.S., also include the annotated U.S. Constitution and annotated federal court rules (See the section on Court Rules & Forms).