A Revenue Ruling (Rev. Rul.) is an official interpretation by the IRS of the Internal Revenue Code, related statutes, tax treaties and regulations. It is the conclusion of the IRS on how the law is applied to a specific set of facts. Revenue rulings are published in the Internal Revenue Bulletin for the information of and guidance to taxpayers, IRS personnel and tax professionals. For example, a revenue ruling may hold that taxpayers can deduct certain automobile expenses. (IRS Website - Understanding IRS Guidance - A Brief Primer )