Libertarianism is sometimes treated as a complicated moral, political, and economic system. While there may be difficult positive applications of it, libertarianism is a simple system of principles.
The non-aggression principle is the fundamental principle of libertarian theory. This principle holds that aggression (the initiation of physical force against persons or their property) is inherently wrong.
Libertarianism is the idea that anything that would be wrong for one man to do to another man by force is wrong for a group of men to do to a man (or group of men) by force.
For every right, there is an equal and opposite responsibility. For the right to his own life, a man has the responsibility of not infringing upon the right to life of another man. To enjoy the right to his own property, a man must not infringe upon the right of any other man to his own property.
To add to his property morally, he must use the means of voluntary exchange, rather than acquiring goods or services by the use of force. He may improve his own estate by homesteading, that is, adding value to property which he has come upon by enhancing it with his labors.
A libertarian society allows men the opportunity to create prosperity and pursue happiness for themselves peacefully. However, what may be prosperity for one man is not necessarily the same for another. So, each individual man in a libertarian society has the right to dispose of his own person and property in the way(s) in which he sees fit. He is allowed to pursue his own happiness.
In pursuing his own happiness, a man may behave immorally, but there should be no legislation against his immoral behavior(s) unless they forcefully take away from another man’s rights to his own person and property. A man may do something ethically wrong, but he has not committed a crime unless and until his actions have a victim (other than “society”), a victim whose right to either life, liberty, or disposal of property has been violated.
With these basic principles in mind, libertarian theory becomes much easier to understand. There are a wide number of sets and sub-sets of theory that fall within the bounds of these simple ideas, but they all maintain these common themes.