The current federal tax law is intertwined with the operations of the Internal Revenue Services, which acts upon the legislative basis created over the years by Congress.
The roots of IRS go back to the Civil War when President Lincoln and Congress, in 1862, created the position of commissioner of Internal Revenue and enacted an income tax to pay war expenses. The income tax was repealed 10 years later. Congress revived the income tax in 1894, but the Supreme Court ruled it unconstitutional the following year.
In 1913, Wyoming ratified the 16th Amendment, providing the three-quarter majority of states necessary to amend the Constitution. The 16th Amendment gave Congress the authority to enact an income tax. That same year, the first Form 1040 appeared after Congress levied a 1 percent tax on net personal incomes above $3,000 with a 6 percent surtax on incomes of more than $500,000.
In 1918, during World War I, the top rate of the income tax rose to 77 percent to help finance the war effort. It dropped sharply in the post-war years, down to 24 percent in 1929, and rose again during the Depression. During World War II, Congress introduced payroll withholding and quarterly tax payments.
1913 Form 1040 (PDF 126KB, 4 pages, including instructions)
A New Name
In the 50s, the agency was reorganized to replace a patronage system with career, professional employees. The Bureau of Internal Revenue name was changed to the Internal Revenue Service. Only the IRS commissioner and chief counsel are selected by the president and confirmed by the Senate.
Today’s IRS Organization
The IRS Restructuring and Reform Act of 1998 prompted the most comprehensive reorganization and modernization of IRS in nearly half a century. The IRS reorganized itself to closely resemble the private sector model of organizing around customers with similar needs.
Source: IRS, http://www.irs.gov/irs/article/0,,id=149200,00.html