Title 26 of the United States Code contains nearly all of the federal tax laws. This title is commonly referred to as the "Internal Revenue Code" (IRC) or sometimes simply as "The Code."
The current version of the Internal Revenue Code is the Internal Revenue Code of 1986, as amended.
The best place to start with specialized tax finding aids is with the relevant IRC section. The IRC is organized logically into subtitles, chapters, subchapters, and parts, each of which contains related provisions on a particular topic. Related sections are often cross-referenced to each other. Therefore, it is often useful to read the table of contents to the Code or to a subchapter in order to get an overview of the structure of a topic.
Generally, each group of related sections will have a section devoted to laying out several definitions. In addition, section 7701 of the Code contains over 50 definitions of terms that are used throughout the Code.
The IRC is organized as follows:
A = Income taxes
B = Estate & gift taxes
C = Employment taxes
D = Misc. excise taxes
E = Alcohol & tobacco excise taxes
F = Procedure & administation
G = The Joint Committee on Taxation
H = Financing of Presidential Campaigns
I = Trust fund code
J = Coal industry health benefits
K = Group health plan benefits
Commonly-researched Subchapters of Subtitle A (income taxes):
A = Determination of tax liability (sections 1--59B)
B = Computation of taxable income (sections 61--291)
C = Corporate distributions and adjustments (corporate tax) (sections 301--385)
J = Income tax on estates and trusts (sections 641--692)
K = Partners and partnerships (partnership tax) (sections 701--777)
S = "S Corporations" (sections 1361--1379)