Final and temporary tax regulations by the IRS (a bureau of the Treasury Department) are extremely helpful in explaining and interpreting the Internal Revenue Code. It is important to locate the relevant Code section first and then find the corresponding Treasury Regulation since there may be more than one regulation pertinent to the Code section in question.  The regulation numbering system is organized to correspond with the sections of the Code.

Most Treasury Regulations go through a process of public notice before they become effective. For Proposed Regulations, there is a thirty day minimum notice / comment  period before becoming final, although typically the process takes much longer.

Once approved, Final Regulations are issued as Treasury Decisions and are announced in the Federal Register and the Internal Revenue Bulletin.  These are consolidated annually into the IRS Cumulative Bulletin and are also compiled under Title 26 of the C.F.R.

Temporary Regulations, also designated as Treasury Decisions, are issued when the IRS needs to address an immediate situation, pre-empting the normal notice / comment period. These regulations have a 3 year time limit.

Listed below are the primary sources for locating tax regulations. Commercial loose-leaf services are another research option.