A political philosophy derived from 18th century political philosophies that were originally designed to justify the ripoff of English peasants by the new upper and middle class.

Libertarians claim that no one should use force unless their property is infringed upon--they tend to ignore the fact that all property was acquired by force in the first place. What they're really saying, following Locke, is that individual property rights should be enforced absolutely, without regard to their impact on others (unless, of course, a conflict can be treated as a clash between two different sets of property rights).

A libertarian society is really a plutocracy, where wealth determines the influence that any given individual will have in government.

There is a neat SF story that depicts a libertarian utopia founded on another planet; ironically, the society depicted also has Marxist elements, since their currency is based on a labor standard and lending at interest is forbidden. However, in a society that is really starting from scratch, libertarianism makes sense. On this planet, it will enforce already existing barriers between wealth and poverty.