The federal tax laws are codified in Title 26 of the U.S. Code but are usually cited and referred to as the Internal Revenue Code "IRC". There have been 3 major codifications: in 1939, 1954, and 1986. Prior to 1939, the tax laws consisted of a series of revenue acts reenacted every 2 or 3 years. The official title of the current U.S. tax law is the Internal Revenue Code of 1986, as amended.
West's Internal Revenue Code also reprints the entire code each year (library has 1954, 1971 to 2002). Tax laws in effect prior to the 1939 code can be found in Internal Revenue Acts of the United States: 1909-1950 (also on HeinOnline).
To compile a legislative history, you can use general sources (see the research guide on Federal Legislative History) or sources that focus solely on tax legislation. Besides the major looseleaf sets, which provide references to, and summaries of, legislative documents, other specialized sources include:
Tax treaties or tax conventions are agreements between countries relating to the treatment of taxpayers who are subject to the tax laws of both countries. The usual purpose of these treaties is to avoid double taxation of income.
For background material on US tax treaties, see: