Consult Finding the Law (12th), Chapter 8(C) "Regulations of Federal Administrative Agencies" for guidance on finding, updating, and verifying regulations using the Federal Register and Code of Federal Regulations.
Consult Fundamentals of Legal Research (10th) Chapter 13 "Administrative Law" for an in-depth look at the history, contents, and uses of the Federal Register system.
For a quick-and-dirty guide to the Federal Register system, consult Legal Research in a Nutshell (13th), Chapter 6 "Administrative Law."
For more information about US publications of Federal rules and regulations before 1935, as well as origins of the Federal Register, see the publications below.
The Federal Register solicits comments from the public. The place those comments are submitted and published is Regulations.gov.
Administrative agencies generate documents and materials beyond the scope of the Federal Register. Use the research guide linked below to find additional administrative documents.