An income tax is a tax levied on the income of individuals or businesses (corporations or other legal entities). Various income tax systems exist, with varying degrees of tax incidence. Income taxation can be progressive, proportional, or regressive. When the tax is levied on the income of companies, it is often called a corporate tax, corporate income tax, or profit tax. Individual income taxes often tax the total income of the individual (with some deductions permitted), while corporate income taxes often tax net income (the difference between gross receipts, expenses, and additional write-offs). Various systems define income differently, and often allow notional reductions of income (such as a reduction based on number of children supported).

The "tax net" refers to the types of payment that are taxed, which included personal earnings (wages), capital gains, and business income. The rates for different types of income may vary and some may not be taxed at all. Capital gains may be taxed when realized (e.g. when shares are sold) or when incurred (e.g. when shares appreciate in value). Business income may only be taxed if it is significant or based on the manner in which it is paid. Some types of income, such as interest on bank savings, may be considered as personal earnings (similar to wages) or as a realized property gain (similar to selling shares). In some tax systems, personal earnings may be strictly defined where labor, skill, or investment is required (e.g. wages); in others, they may be defined broadly to include windfalls (e.g. gambling wins).

Milton Friedman (July 31, 1912 – November 16, 2006) was an American economist, statistician, and author who taught at the University of Chicago for more than three decades. He was a recipient of the Nobel Memorial Prize in Economic Sciences, and is known for his research on consumption analysis, monetary history and theory, and the complexity of stabilization policy. As a leader of the Chicago school of economics, he influenced the research agenda of the economics profession. A survey of economists ranked Friedman as the second most popular economist of the twentieth century behind John Maynard Keynes, and The Economist described him as "the most influential economist of the second half of the 20th century…possibly of all of it."

Friedman's challenges to what he later called "naive Keynesian" (as opposed to New Keynesian) theory began with his 1950s reinterpretation of the consumption function, and he became the main advocate opposing activist Keynesian government policies. In the late 1960s he described his own approach (along with all of mainstream economics) as using "Keynesian language and apparatus" yet rejecting its "initial" conclusions. During the 1960s he promoted an alternative macroeconomic policy known as "monetarism". He theorized there existed a "natural" rate of unemployment, and argued that governments could increase employment above this rate (e.g., by increasing aggregate demand) only at the risk of causing inflation to accelerate. He argued that the Phillips curve was not stable and predicted what would come to be known as stagflation. Friedman argued that, given the existence of the Federal Reserve, a constant small expansion of the money supply was the only wise policy.

William Henry "Bill" Gates III (born October 28, 1955 in Seattle, Washington) is an American business magnate, computer programmer and philanthropist. Gates is the former chief executive officer (CEO) and current chairman of Microsoft, the world’s largest personal-computer software company he co-founded with Paul Allen. He is consistently ranked among the world's wealthiest people and was the wealthiest overall from 1995 to 2009, excluding 2008, when he was ranked third; in 2011 he was the wealthiest American and the second wealthiest person. During his career at Microsoft, Gates held the positions of CEO and chief software architect, and remains the largest individual shareholder, with 6.4 percent of the common stock. He has also authored or co-authored several books.

Gates is one of the best-known entrepreneurs of the personal computer revolution. Gates has been criticized for his business tactics, which have been considered anti-competitive, an opinion which has in some cases been upheld by the courts. In the later stages of his career, Gates has pursued a number of philanthropic endeavors, donating large amounts of money to various charitable organizations and scientific research programs through the Bill & Melinda Gates Foundation, established in 2000.

Irwin A. Schiff (born in February 24, 1928) is a prominent figure in the United States tax protester movement. Schiff is known for writing and promoting literature that claims the United States income tax is applied incorrectly. He has lost several civil cases against the federal government and has a record of multiple convictions for various federal tax crimes. Schiff is serving a 13-plus year sentence for tax crimes (with his location listed as the Terre Haute Federal Correctional Institution). His projected release date is October 7, 2016. Schiff is the father of stockbroker and former United States Senate candidate Peter Schiff.

In 1950, Schiff graduated from the University of Connecticut with a Bachelor of Science degree in accounting and economics.

After college, Schiff was in the insurance brokerage business in Connecticut. In connection with his business, he was involved in a tax shelter in which he became the victim of a Ponzi scheme in which he lost his money and the money of his clients. In 1968 he testified before the Senate Committee on Banking and Currency in opposition to the removal of gold backing from Federal Reserve Notes. In 1976, he published a book entitled The Biggest Con: How the Government is Fleecing You. Schiff was a candidate for the Libertarian Party presidential nomination in 1996, and he participated in a Libertarian Party debate in Washington on July 5, 1996.

Tommy K. Cryer, also known as Tom Cryer (born September 11, 1949 in Lake Charles, Louisiana), is an attorney in Shreveport, Louisiana who was charged with and later acquitted of willful failure to file U.S. Federal income tax returns in a timely fashion. In a pending case in United States Tax Court, Cryer is contesting a determination by the U.S. Internal Revenue Service that he owes $1.7 million in taxes and penalties.

According to a resume published by Cryer on his website, Cryer graduated with honors from Louisiana State University (LSU) Law School in 1973, and was inducted into the LSU Law School Hall of Fame in 1987. Cryer is also a member of the Order of the Coif (a law school honor society), that he served as a Special Advisor and Draftsman at the Louisiana Constitutional Convention in 1973 and that he has argued cases before the Louisiana Supreme Court. Finally, he opened a solo law practice in 1975 and gained experience in many different civil and criminal matters.

On his web site Cryer makes a variety of assertions about the legality of the federal income tax in the United States, mostly in regard to taxes on wages. He claims that "the law does not tax [a person's] wages", and that the federal government cannot tax "[m]oney that you earned [and] paid for with your labor and industry" because "the Constitution does not allow the federal government to tax those earnings" (referring to "wages, salaries and fees that [a person] earn[s] for [himself]"). Cryer states: