Congress writes tax laws, but it's the job of the Internal Revenue Service (IRS) to implement them. In other words, Congress set the rules, but the IRS has to explain how those rules are applied in different situations. It does this primarily through Treasury Regulations and Revenue Rulings, written regulations and procedures that are four times as long as the tax code itself [sources: U.S. Census Bureau and Nolo.com].
The IRS is also primarily responsible for enforcing tax laws and regulations. Filing and paying income tax is "voluntary," meaning the IRS allows individuals and businesses to calculate what they owe. But paying taxes isn't optional; it's right there in Title 26 of the U.S. code [source: Internal Revenue Service]. Still, many Americans choose not to pay taxes. In fact, Americans owed $330 billion in unpaid taxes by the end of 2010 [source: U.S. Government Accountability Office].
If you don't pay your taxes, the IRS will initiate a collection process. The process starts with a bill in the mail. If you fail to pay or file for an extension or installment plan, the IRS will send collection agents to seize your assets [source: IRS]. If the IRS finds irregularities in your tax filings, it will issue an audit of your financial records. Taxpayers have the right to fight any decision by the IRS and file a petition in U.S. Tax Court [source: U.S. Tax Court].
The IRS also comes after people who exploit the tax system for criminal purposes. Special agents with the IRS Criminal Investigations division go after individuals and corporations that try to evade taxes through fraudulent filings or record keeping [source: IRS]. The IRS also investigates money-laundering schemes where criminals try to hide income from illegal sources. Remember that Al Capone was convicted of tax evasion, not murder or racketeering. Such criminal tax cases are heard by federal courts and can be appealed all the way to the Supreme Court [source: Nolo].
For lots more information on taxes, tax cheats and tax history, see the links on the next page.