Federal agencies promulgate rules and regulations by authority of the executive branch of government or statutory grant. Most agency actions are governed by the Administrative Procedures Act, codified in Title 5 of the United States Code. Agency rules and regulations are first published in the Federal Register, a chronological publication (Fed. Reg. or FR), and then codified in the Code of Federal Regulations (CFR).
In addition to the resources below, the FR and CFR can be found in Lexis Advance/Lexis Academic, Westlaw, and Bloomberg Law.