A Revenue Ruling is an official interpretation by the IRS of the Code, related statutes, tax treaties, and regulations. It explains the IRS's position on how the law is applied to a specific set of facts.
Any taxpayer whose circumstances are substantially the same as those described in the Ruling can rely on it.
A Revenue Procedure is an official statement of a procedure that affects the rights or duties of taxpayers under the Code, related statutes, regulations, and treaties that should be a matter of public knowledge. Generally, it provides instructions for return filing or other procedures. Sometimes it may have a substantive effect (e.g., interest rate tables).
Notices provide interim guidance before finalized revenue rulings and regulations are available.
Announcements are public pronouncements that have only immediate or short-term value (e.g., extension of filing deadlines for areas hit by natural disasters).
The Internal Revenue Bulletin (I.R.B.) is published weekly and compiled semi-annually into the Cumulative Bulletin (C.B.). Note that the C.B. ceased publication in 2008.