The United States has a voluntary tax reporting system. Once a tax return is filed, however, the IRS will seek to verify that filed tax returns comply with the tax laws. To achieve this, an IRS audit ("examination") must take place. There are different types of IRS audits.
The most common type of IRS audit is a "correspondence audit" conducted entirely through the mail. Most correspondence audits are initiated by the IRS computer system, which receives income information for individuals reported to the IRS by third parties (e.g., Form W-2 wages/salaries from employers; Form 1099 ...