This article seeks to uncover the philosophical background of the liberal argument in favour of freedom of expression, and to distinguish it from the philosophical background of the republican approach to this freedom. Crucially, the republican approach gives prominence to collective civic values and virtues over individual rights and tends to limit freedom of expression to what those values and virtues find acceptable. In contrast, the liberal approach is distinguished by its individualistic character and its defence of freedom of expression as a fundamental individual right that may only be restricted in service of this freedom, not of collective goals. Further, the article unpacks the various arguments developed by the liberal tradition to legitimise freedom of expression, in accordance with the ethical theories of liberal philosophers, and will assess the strengths and weaknesses of each argument. Finally, the article discusses the relevance of the principle by which liberalism justifies the limitation of freedom of expression. Crafted by John Stuart Mill, the "harm principle" prevents individual expression only when there is evidence that doing so would cause material harm to others. This paper argues that recent events faced by democratic societies prove that the harm principle is insufficient and supports the calls of philosopher Joel Feinberg (1926–2004) for its supplementation with the "offence principle", where individuals are protected by law from offences as well as harms.