A regulation is issued by the Internal Revenue Service and Treasury Department to provide guidance for new legislation or to address issues that arise with respect to existing Internal Revenue Code sections. Regulations interpret and give directions on complying with the law.
Regulations are published in the Federal Register. Generally, regulations are first published in proposed form in a Notice of Proposed Rulemaking (NPRM). After public input is fully considered through written comments and even a public hearing, a final regulation or a temporary regulation is published as a Treasury Decision (TD), again, in the Federal Register.