Although liberalism and libertarianism share some important characteristics (strong emphasis on equality before the law and civil rights), they're not the same thing.

Notably, libertarianism can be left-wing in a way that liberalism cannot (e.g. anarcho-syndicalism, anarcho-communism, green politics, etc.). Some left-libertarians even reject the concept of private property entirely.

Liberalism doesn't completely overlap with right libertarianism, either. Liberals are more willing to accept some authoritarian ideas, such as e.g. having a military to protect trade.