The subject of this Essay is not the so-called Liberty of the Will, so unfortunately opposed to the misnamed doctrine of Philosophical Necessity; but Civil, or Social Liberty: the nature and limits of the power which can be legitimately exercised by society over the individual. (...) The only purpose for which power can be rightfully exercised over any member of a civilised community, against his will, is to prevent harm to others.In this famous essay, John Stuart Mill questions liberty of thought, individualism and the limits to the authority of society over the individual. The text is here followed by "Utilitarianism", a treatise in which he defines the main lines of this moral and political theory based on the greatest happiness of the greatest number.