Libertarianism is a political philosophy that believes in minimizing or entirely eliminating government interventionism in many aspects of life including economic, personal, and in foreign policy matters. Libertarians tend to oppose legal restrictions on social behavior that is considered by many to be immoral. The French term of Laissez-Faire, or let us do, is a term that describes some aspects of the libertarian belief.  Libertarianism tends to emphasize a form of individual liberty, and tends to support rights of private property.
The first systematic libertarian was Herbert Spencer (1820-1903), an English political philosopher whose books such as The Man Versus the State (1884) had a major impact in Europe and America in the late 19th century. The chief American representative was Yale professor William Graham Sumner.
Ronald Reagan stated in 1975, "I believe the very heart and soul of conservatism is libertarianism....The basis of conservatism is a desire for less government interference or less centralized authority or more individual freedom and this is a pretty general description also of what libertarianism is....Now, I can’t say that I will agree with all the things that the present group who call themselves Libertarians in the sense of a party say, because I think that like in any political movement there are shades, and there are libertarians who are almost over at the point of wanting no government at all or anarchy. I believe there are legitimate government functions. There is a legitimate need in an orderly society for some government to maintain freedom or we will have tyranny by individuals."
In the United States, libertarians are typically fiscally conservative and socially liberal using the common US meanings of liberal and conservative. A faction of libertarians exist in the GOP, and are typically more ardent than other members of the GOP in keeping the principle of fiscal sanity and are less willing to "sell out" those principles for political expediency. They support an isolationist foreign policy and are to the left of most Democrats on social and foreign policy issues. The foremost libertarian figure in the GOP is former long-time Congressman Ron Paul.
Libertarianism is best summed up in the Non-Aggression Principle, which states that government (or "private police agencies" in the anarcho-capitalist variant) should only exist to protect life, liberty, and property from force and fraud.
Libertarianism is closely related to liberalism, if this word is interpreted according to its original meaning of classical liberalism. Libertarians in America tend to be liberal on social issues but conservative on economic issues. Libertarians generally oppose government regulation of drugs, prostitution, and marriage (including bans of same-sex marriage. The Libertarian Party officially supports legalized abortion, however, libertarians themselves are divided on the issue, since government protection from force depends on the personhood of the unborn baby (or fetus). However, libertarians are uniformly opposed to government funding for abortions (such as through Planned Parenthood). Furthermore, they oppose restrictions on pornography. However, they also oppose universal health care, taxes and the welfare state. They are strong supporters of school choice, and oppose continuing the public school system. Some libertarians support school vouchers, while others are skeptical due to the issue of government influence over private education.
Libertarians support an expansive view of liberty as the proper basis for organizing civil society. They tend to define liberty as the freedom to do whatever one wishes up to the point that one's behavior begins to interfere with another's person or property through coercive means. At the point of interference, each party would become subject to certain principled rules for adjudicating disputes, generally accepting that one who has demonstrated a proven lack of respect for the rights of others should be subject to sanctions, including possible constraints on their freedom. They believe that liberty is the right of every individual.
Libertarians generally defend the ideal of freedom from the perspective of how little one is constrained by authority, i.e., how much one is allowed to do (also referred to as negative liberty). This ideal is distinguished from a view of freedom focused on how much one is able to do (also called positive liberty).
Libertarians tend to use the word "libertarian" (small "l") to refer to the philosophy, and "Libertarian" (capital "L") to refer to the party. Thus, more libertarians exist than members of the Libertarian Party. Two general factions exist in the libertarian movement. The first are those libertarians who apply the principles of right to person and property to an absolute. They believe that no person, group, or government is above the right to violate these two things. They thus believe that government itself is illegitimate because it violates person and property. These libertarians subscribe to anarcho-capitalism, as first named by Murray N. Rothbard. They believe that law and security can be handled by private means in the free market. The other faction believes in a very limited government. They are often referred to as minarchists. Libertarian minarchists want the state to only enforce law and order but generally nothing else. Ayn Rand was a minarchist.
Libertarians tend to view liberalism as a philosophy advocating less government interference in private morality and more government control of business, and view conservatism as a philosophy advocating more government interference in private morality and less government control of business, while they view libertarianism as advocating less government control in all areas. However, there have been fusionist attempts to mix libertarianism and with social conservatism. This is noted in particular by paleolibertarians. They believe that social conservatism is a natural entity in a free society, but do not believe that it can be enforced by state interventionism. For instance, they may personally oppose homosexuality, but advocate for marriage privatization rather than believing that government should sanction "marriage" exclusively between a man and a woman.
Outside the United States, the term "libertarian" refers to left-wing anarchism.
Libertarian Thought in America
While there are libertarian factions within the Democratic and Republican parties, neither party is particularly well aligned with libertarian thought. While the Republican Party sometimes adopts libertarian-sounding rhetoric of small government in economic affairs, many libertarians see it as being a force that has increased government interventionism in these affairs. Libertarians generally, for example, are opposed to the USA PATRIOT Act, which they believe increases government power and removes protections on the liberty and privacy of the public. Most conservatives, on the other hand, view it as a necessary government program and believe security to be more important than personal liberty and privacy. Libertarians point out that such a view contradicts those of the founding fathers, such as Benjamin Franklin, who summarized it most eloquently, "Those who would give up Essential Liberty to purchase a little Temporary Safety, deserve neither Liberty nor Safety." Libertarians are also generally opposed to the Iraq War, unlike the majority of conservatives.
While all libertarians agree in general on the principles of the desirability of maximizing individual liberty and avoiding excessive government interference with the operation of the free market, individual libertarians have opinions that differ wildly within these general principles.
The libertarian movement generally praises the United States Constitution, regarding it as the proper scope of the national government. They believe that the Democratic and Republican parties have overstepped constitutional limits. Anarcho-capitalist libertarians, on the other hand, view the implementation of the constitution as the very reason the national government is the size it is today.
Libertarian-oriented writers include Frédéric Bastiat, William Leggett, John Stuart Mill, Henry David Thoreau, Lysander Spooner, Herbert Spencer, William Graham Sumner, Carl Menger, Ludwig von Mises, Rose Wilder Lane, Albert Jay Nock, Henry Hazlett, and Isabel Paterson.
- Ron Paul, Republican congressman from Texas, 1988 Libertarian Party and 2008 & 2012 Republican Party presidential candidate. Ron Paul is considered to be of the Constitutionalist and paleolibertarian schools of libertarian thought.
- Gary Johnson, businessman, former Governor of New Mexico (as a Republican), and 2012 Libertarian Party nominee.
- The psychiatrist Thomas Szasz, opponent of the therapeutic state and compulsory mental institutionalization.
- Nobel Laureate economists Milton Friedman, F.A. Hayek, Ronald Coase, Gary Becker, James Buchanan, George Stigler, and Vernon Smith.
- The novelist Ayn Rand advocated a philosophy of Objectivism, embodying some libertarian thought, although differing from libertarianism in many ways. Some of her novels, such as Atlas Shrugged, have become icons of some people in the libertarian movement, while others find her materialism and atheism incompatible with moral ethics and natural rights and law.
- Robert LeFevre, significant in promoting libertarian philosophy in the 1950s and 1960s before it was a well-defined movement, with his "Freedom School" seminars on political and economic philosophy.
- Karl Hess, speechwriter for Barry Goldwater credited with penning Goldwater's famous 1964 statement "Extremism in the defense of liberty is no vice". Hess later became a major figure in the Libertarian Party.
- Murray N. Rothbard was nicknamed "Mr. Libertarian." He brought to life the anarcho-capitalist movement. Rothbard was an economist of the Austrian School.
- Samuel Edward Konkin III, a significant figure in 1970s libertarianism, whose influence waned considerably after the rise of the Libertarian Party as he opposed political parties and voting as being against libertarian principles. He proposed instead a purely marketplace-based route to a free society, such as tax resistance and doing business "off the books".
- Robert A. Heinlein, science fiction author, whose 1966 novel The Moon Is A Harsh Mistress was an influence on the movement.
- L. Neil Smith, J. Neil Schulman, and Brad Linaweaver, science fiction writers.
- Several popular financial writers including Harry Browne and Howard J. Ruff. Browne would later run for President, twice, on the Libertarian Party ticket. Ruff declared his political philosophy as libertarian but as a socially conservative Mormon made an exception on issues like abortion and prostitution, where he disagreed with the libertarian view.
- Penn and Teller, stage magicians turned libertarian evangelists preaching atheism and promoting libertarian philosophies, including controversial positions such as legalization of prostitution and drugs in their Showtime series, which sports a name that cannot for reasons of good taste be expressed here.
- The Canadian rock band Rush, which has been together since 1968, often explores libertarian themes in their lyrics, like in "Free Will", "Tom Sawyer" and "Something for Nothing". Drummer and Lyricist Neil Peart claims to be a "left leaning libertarian." ,
- Humorist Dave Barry, actor/comedian Drew Carey, actor Denis Leary, former MTV VJ Lisa "Kennedy" Montgomery, actor Kurt Russell, investigative reporter John Stossel, and the late rocker Frank Zappa have all referred to themselves as being aligned with or openly supporting the Libertarian Party.
- Trey Parker and Matt Stone, the creators of South Park, proclaimed that they are libertarians. South Park is vulgar, supports evolution, and sometimes attacks social conservative positions like religion. However, they also make fun of liberals' positions such as political correctness, environmentalism and atheism. . The phrases "South Park Conservative" (the name of a book) and "South Park Republican" are used to describe the followers of these beliefs.
- Ed Clark, the Libertarian Party's 1980 nominee for President. Clark obtained the highest popular vote percentage to date for a Libertarian candidate.
- Many Republican congressmen and senators hold libertarian positions, such as Walter B. Jones, Rand Paul and Justin Amash.
- Barry Goldwater, Republican presidential nominee in 1964 often described himself as libertarian, although whether or not this was true has been disputed by conservatives.
- Glenn Beck, political commentator, describes himself as a libertarian
- Libertarian FAQ
- Open Directory libertarian links
- Black Libertarians
- Libertarian Wiki
- Libertarians for Life
- The Independent Institute
- Ludwig von Mises Institute
- Foundation for Economic Education
- Cato Institute
- Reason Foundation
- Boaz, David. The Libertarian Reader: Classic and Contemporary Writings from Lao Tzu to Milton Friedman (1998) excerpt and text search
- Doherty, Brian. Radicals for Capitalism: A Freewheeling History of the Modern American Libertarian Movement (2008) excerpt and text search
- Hamowy, Ronald, ed. The Encyclopedia of Libertarianism (Sage, 2008), 644pp, sponsored by the Cato Institute; Online at some academic libraries also excerpt and text search
- Murray, Charles. What It Means to Be a Libertarian (1997) excerpt and text search
- Tilman, Rick. Ideology and Utopia in the Social Philosophy of the Libertarian Economists (2001) excerpt and text search
- "Libertarians are neither. Unlike Liberals or Conservatives, Libertarians advocate a high degree of both personal and economic liberty. For example, Libertarians advocate freedom in economic matters, so we're in favor of lowering taxes, slashing bureaucratic regulation of business, and charitable -- rather than government -- welfare. But Libertarians are also socially tolerant. We won't demand laws or restrictions on other people who we may not agree because of personal actions or lifestyles. Think of us as a group of people with a "live and let live" mentality and a balanced checkbook." 
- Chris Matthew Sciabarra, "The First Libertarian," Liberty (Aug 1999) online
- see "Inside Ronald Reagan: A Reason Interview" (July 1975)
-  Parker and Stone, Reason Magazine