What's the Primary Sources of Tax Law in United States?

• The Law = Internal Revenue Code of 1986 as Amended (IRC)
        The statutory source of tax law is the Internal Revenue Code of 1986 as Amended (IRC). Even though it is called the 1986 IRC, this does not mean that the laws are from 1986. This is just the last time that Congress changed the name of the Code. A law passed in the current year will amend the IRC of 1986 and be found in the IRC of 1986.

• Prior Internal Revenue Codes were the IRC of 1939 and the IRC of 1954.  When the 1954 Code was created, Code sections numbers were changed. For example, § 108 in the 1939 Code is §21 in the 1954 & 1986 Code. The updating of the code name from 1954 to 1986 did not involve changing any Code section numbers; it was just a radical change in the law.

• Interpretations = Treasury, IRS, Courts
        Primary interpretations are provided by the government, such as the Treasury Department, the IRS, and the Courts. Primary sources are the only type of interpretation that can be used to support a tax position when in discussion with the IRS. Secondary sources hold no weight with the IRS or Courts.