Libertarianism includes a broad spectrum of political philosophies, each sharing the common overall priority of minimal government combined with optimum possible individual liberty. Its goals prioritize freedom: freedom of speech, freedom of assembly, freedom to bear arms, freedom of and from religion, freedom of the Press, freedom of ownership and economic freedom. It promotes personal responsibility and private charity, as opposed to the provision of welfare services by the state, and it rejects the compulsions of Socialism and Communism.

Individual Libertarians may differ considerably over particular issues and, although there are Libertarian political parties worldwide, even these differ significantly in their outlooks and policies. There is also a significant disparity between the usage of the term in the United States (where it is often considered synonymous with Liberalism and Individualism in general, and Conservatism in particular, especially insofar as it supports limited government) and elsewhere (where it is more often understood to refer to radical leftist currents of Anarchism).

Generally speaking, Libertarians 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 (negative liberty), as opposed to the opportunity and ability to act to fulfill one's own potential (positive liberty), a distinction first noted by John Stuart Mill. They view life, liberty and property as the ultimate rights possessed by individuals, and that compromising one necessarily endangers the rest. They consider compromise of these individual rights by political action to be "tyranny of the majority", a term first coined by Alexis de Tocqueville (1805 - 1859), and made famous by John Stuart Mill. Many Libertarians would also argue, however, that representative majority rule democracy has largely become controlled by special interest groups who represent a minority, leading to a "tyranny of the minority" against the real numerical majority.

The term "libertarian" stems from the French word "libertaire" ("for liberty"), and its first recorded use in a political sense was in 1857 by Anarcho-Communist Joseph Déjacque (1821 -1864). In common usage, "libertarian" refers to a person who advocates liberty, especially with regard to thought or conduct, or a person who maintains the doctrine of free will.

The history of Libertarianism is also the history of classical Liberalism, and the two concepts are very closely related. The initial theory arose from Enlightenment ideas in 18th Century Europe and America, especially the political philosophies of John Locke and the Baron de Montesquieu (1689 - 1755), and the moral and economic philosophy of Adam Smith.

Locke believed that the role of any legislature was to protect natural rights in the legal form of civil rights. He proposed a labour theory of property whereby each individual owns the fruits of his efforts by virtue of his labour, and from this an economy emerges based on private property and trade, with money as the medium of exchange.

At around the same time, the French philosopher Montesquieu developed a distinction between sovereign and administrative powers, and proposed a separation of powers (usually into the Executive, the Legislative and the Judicial) to act as a counterweight to the natural tendency of administrative power to grow at the expense of individual rights. This became an important concept in both constitutional monarchies and republics.

Adam Smith's moral philosophy stressed government non-intervention so that individuals could achieve whatever their "God-given talents" would allow without interference from arbitrary forces. He also opposed trade guilds (fore-runners to modern unions) and joint stock companies (or corporations) for the same reasons.

The Founding Fathers of the United States enshrined the protection of liberty as the primary purpose of government in the Declaration of Independence of 1776 and the United States Constitution, and Thomas Jefferson (1743 - 1826) in particular was key in etablishing the Law of Equal Liberty and the Non-Aggression Principle as major tenets. Very similar ideas were also included in the French Declaration of the Rights of Man and Citizen of 1789, a key document in the French Revolution.

John Stuart Mill declared that his preferred doctrine of Utilitarianism requires that political arrangements satisfy the "liberty principle", whereby each person is guaranteed the greatest possible liberty that would not interfere with the liberty of others, in order maximize happiness.

In the late 19th Century and early 20th Century, Progressivism in the United States and Socialism in Europe increasingly focused on the advancement of workers' rights and social justice to counteract the increasing excesses of rampant Capitalism and industrialism. It was only in the latter half of the 20th Century that the term "libertarian", which had earlier been associated with Anarchism, came to be adopted by those whose attitudes bore closer resemblance to classical liberals.

Libertarianism is usually split into two main types:

• Rights Libertarianism (or Rights Theory or Libertarian Moralism or Deontological Libertarianism):
  Rights Theorists assert: 1) that: all persons are the absolute owners of their lives, and should be free to do whatever they wish with their own bodies or property, provided they do not infringe on the rights of another to do the same (the Law of Equal Liberty); and 2) that aggression, or the initiation of physical force or the threat of such, against a person or his property, is inherently illegitimate insofar as it impinges on on the equal rights of a person (the Non-Aggression Principle), except in the case of self-defence. This view of "natural rights" derives from the early writings of Thomas Hobbes and John Locke.
  Most Rights Libertarians recognize the necessity of a limited role of government as a "necessary evil" to protect individuals from any violation of their rights, and to prosecute those who initiate force against others (Minarchism), although some oppose the existence of government and taxation altogether on the grounds that it represents aggression against individual rights by its very nature (Anarcho-Capitalism).
  Robert Nozick (1938 -2002) and Murray Rothbard (1926 - 1995) are representatives of this view of Libertarianism.

• Consequentialist Libertarianism (or Libertarian Consequentialism)
  Consequentialist Libertarians justify the rights of individuals on pragmatic or consequentialist, as well as moral, grounds (Consequentialism is the moral theory that the consequences of a particular action form the basis for any valid moral judgment about that action). They are less concerned with the Non-Aggression Principle and more concerned with the notion of a society that allows individuals to enjoy political and economic liberty, which they see as the foundation for human happiness and prosperity. They argue that individual liberty leads to economic efficiency and other benefits, and is thus the most effective means of promoting or enhancing social welfare.
  Milton Friedman (1912 - 2006), Ludwig von Mises (1881 - 1973), and Friedrich Hayek (1899 - 1992) are major proponents of this view.

Another split is between left-wing and right-wing Libertarianism:

• Left-Libertarianism (or Geolibertarianism):
  Left-Libertarianism combines a strong commitment to personal liberty with an egalitarian view concerning natural resources, believing that it is not legitimate for someone to claim private ownership of resources to the detriment of others, and that each individual is entitled to an equal share of natural resources. Many Left-Libertarians advocate strong alliances with the Left on issues such as the anti-war movement and labour unions, and some wish to revive voluntary cooperative ideas such as mutualism.
  • Agorism is an extreme form of Anarcho-Capitalism and Libertarianism, developed by Samuel Edward Konkin III (1947 - 2004) and building on the ideas of Murray Rothbard (1926 - 1995), which takes as its ultimate goal a society in which all relations between people are voluntary exchanges, a completely free market in an underground or "counter economy" in which the State is redundant (Anarchism). Agorists consider themselves Left-Libertarians, although there is contention over that.
• Right-Libertarianism (or Libertarian Conservatism):
  Right-Libertarianism is synthesis of Libertarianism and right-wing conservatism, and stresses limited government and strong Capitalism. It differs from some Christian-influenced conservativism in that it generally favours the separation of church and state. It is sometimes split into four main branches:
  
  • Classical or Traditional Libertarianism, whose main goals are the shrinking of the power of government and the promotion of free markets, and generally believes that social liberalism and anti-militarism promote economically conservative goals.
  • Neolibertarianism, which, in opposition to Classical Libertarianism, supports an interventionist foreign policy and militarism to expand democracy.
  • Paleolibertarianism, a more culturally conservative and ardently Christian view than Classical Libertarianism, usually involving views against abortion and for the complete privatization of education.
  • Small Government Conservatism, a socially conservative outlook which generally considers any necessary government enforcement the responsibility of state governments, not the federal government.