Regulations are promulgated by executive department and agencies. They are collected in the Code of Federal Regulations and categorized by subject matter. They are cited as TITLE C.F.R. SECTION -- for example 21 C.F.R. § 500.51 refers to Title 21 (Food and Drugs) Code of Federal Regulations Section 500.51 (Labeling of animal drugs; misbranding).
The official site for U.S federal regulations is Regulations.gov.