A statute is the law as passed by the U.S. Congress or a State Legislature.
Statutory laws are published in two forms: A chronological form exactly as passed by the legislature, and a codified form, which arranges the law by topic and removes all superseded and repealed laws. Codified statutes are referred to as a "code,"
Regulations are the detailed rules which articulate how statutes will be enforced. They have the force of law.
Regulations are created by administrative agencies of the executive branch of government.
Regulations are also generally published in two versions: Chronologically, and codified--which arranges the regulations by subject.
Courts interpret statutes and regulations.
Broadly speaking, there are are two types of courts: trial courts and appeals courts.
Findings of fact and law are made in the trial court. These findings or decisions may be appealed to an appeals court, which has the power of review. Appeals courts, appellate courts or a court of appeals determine whether statutes and regulations have been applied fairly and correctly in trial courts or a lower appeals court.
Opinions rendered by appeals court decisions constitute the body of case law, which continually evolves as courts interpret laws and regulations.
Sources for tax case law:
Administrative Rulings, or revenue rulings, are public administrative rulings by the Internal Revenue Service (IRS). They apply the law to issues or situations not addressed by the code, regulations, or case law. Public administrative rulings are subordinate to the Internal Revenue Code and other statutes, Treasury regulations, treaties and court decisions.
Sources for Administrative Rulings: