The Internal Revenue Service (IRS), which administers the income tax, is part of the U.S. Department of Treasury. Adapting to changes in technology to achieve the most efficient processing of information is a major challenge for the IRS. For many years the IRS was organized on a geographical basis, but in 1998 it was reorganized into four functional divisions differentiated by type of taxpayer.

For corporate and individual taxpayers that report on a calendar-year basis, annual tax returns are due on or before March 15 and April 15, respectively, following the close of the calendar year. Providing that the tax due is paid, time extensions for filing returns may be obtained. Although the closing dates for the quarters differ, both individuals and corporations are subject to the payment of estimated tax in quarterly installments. Taxpayers who fail to file tax returns or fail to pay taxes are subject to monetary penalties, fines, and possibly prison sentences.

Extention of income tax to the state level

Wisconsin was the first state to adopt an income tax in 1911. Massachusetts and New York soon followed by adopting income taxes when faced with problems related to World War I. Most other states adopted the income tax as a response to revenue crises created by the Great Depression. » Read more: Administration of federal income tax