Libertarianism is grounded in the belief that Negative Liberty is paramount. You are free to do as you wish, use and dispose of your property as you wish, (including your body), provided that you do not interfere with the Liberties of others in the process.
The result of this is that you are both free to act and responsible for those actions. You are free to get drunk for instance but if you hit someone while inebriated you are just as guilty as if you had done so while sober.
Libertarianism, almost by definition, requires a small government. Large enough to enforce justice and defend against those who would interfere with your rights but not so large as to spend its time interfering itself.
Do go and read the whole pithy post...