What is the Non-Aggression Principle?

The Non-Aggression Principle (NAP) is THE core libertarian idea that says — Don’t aggress or initiate force against anyone, personally or politically.

Murray Rothbard states:

“The libertarian creed rests upon one central axiom: that no man or group of men may aggress against the person or property of anyone else. This may be called the "nonaggression axiom." "Aggression" is defined as the initiation of the use or threat of physical violence against the person or property of anyone else. Aggression is therefore synonymous with invasion” (1)

According to the NAP, violence can only be used in defense of oneself and/or others:

".... Violence may be employed only against the man who commits such violence; that is, only defensively against the aggressive violence of another. In short, no violence may be employed against a nonaggressor. Here is the fundamental rule from which can be deduced the entire corpus of libertarian theory." (2)

The Non-Aggression Principle originates from property rights. Stephen Kinsella states:

“The nonaggression principle is ... dependent on property rights, since what aggression is depends on what our (property) rights are. If you hit me, it is aggression because I have a property right in my body. If I take from you the apple you possess, this is trespass — aggression — only because you own the apple. One cannot identify an act of aggression without implicitly assigning a corresponding property right to the victim.” (3)

What it all means:

• Let each individual live as he/she wills, provided he/she permits the same to others.
• Do not use force except for defensive purposes.
• The victim of aggression is the person whose property rights are violated. And where there is no victim, there is no crime.

Libertarians want a world where force is used only defensively — no aggression!

References:

1. Rothbard, “For A New Liberty” 
2. Rothbard, “War, Peace, and the State” (1963)
3. Kinsella, “What Libertarianism Is”