The first paragraph of this article is almost perfect:
libertarianism, political philosophy that takes individual liberty to be the primary political value. It may be understood as a form of liberalism, the political philosophy associated with the English philosophers John Locke and John Stuart Mill, the Scottish economist Adam Smith, and the American statesman Thomas Jefferson. Liberalism seeks to define and justify the legitimate powers of government in terms of certain natural or God-given individual rights. These rights include the rights to life, liberty, private property, freedom of speech and association, freedom of worship, government by consent, equality under the law, and moral autonomy (the ability to pursue one’s own conception of happiness, or the “good life”). The purpose of government, according to liberals, is to protect these and other individual rights, and in general liberals have contended that government power should be limited to that which is necessary to accomplish this task. Libertarians are classical liberals who strongly emphasize the individual right to liberty. They contend that the scope and powers of government should be constrained so as to allow each individual as much freedom of action as is consistent with a like freedom for everyone else. Thus, they believe that individuals should be free to behave and to dispose of their property as they see fit, provided that their actions do not infringe on the equal freedom of others.
The remainder of the essay is pretty good, too, in that it traces the concept of self-ownership through history in a way that gives libertarian principles a venerable pedigree.
The concept of liberty strikes me as one of the great innovations of the human race. Human or natural rights aside, the opposite concept is the concept of tyranny. If I had to choose one or the other based on foreseeable benefits, I’d choose liberty.