Tax law is found in many places - tax law is generated by the federal government, state government as well as counties, cities, and other municipalities. The variety of taxes that everyone faces is staggering - tax law affects almost every aspect of your life.
As for federal taxes, the law is primarily found in:
Title 26 of the United States Code - the Internal Revenue Code of 1986 as amended (the "Code" as promulgated by the Congress of the United States),
Title 26 of the Code of Federal Regulations (the "Regulations" as promulgated by the Internal Revenue Service),
proposed regulations issued by the Internal Revenue Service ("IRS"),
temporary regulations issued by the IRS,
revenue rulings issued by the IRS,
private letter rulings issued by the IRS,
revenue procedures, policy statements, and technical information releases issued by the IRS, and
federal tax court decisions.
Tax law for states, counties, cities and other municipalities is likewise contained in codes sections, regulations, administrative codes, procedures and statements issued by the respective government authorities, as well as state court decisions. In many instances, state law is patterned after federal law but this is not necessarily always the case.
Tax law is pervasive throughout our daily lives. A lot of trees have been turned into pages of tax law. As you ease into your research of tax law, try to see the forest without getting lost in all the trees.
In a nutshell, tax law is a bewildering array of law that is scattered throughout many different sources and subject to many interpretations.