This chapter explores the theory that, to avoid the ‘tyranny of the majority’, we should be given the liberty to act just as we wish, provided that we do no harm to others. The focus is on John Stuart Mill’s Liberty Principle (also known as the Harm Principle), according to which you may justifiably limit a person’s freedom of action only if they threaten harm to another. The chapter considers Mill’s arguments based on the Liberty Principle, including his claim there should be complete freedom of thought and discussion, and that harming another’s interests is not a sufficient condition to justify constraint. It also discusses justifications for the Liberty Principle by focusing on issues of rights and utility, individuality and progress, and liberty as an intrinsic good. It concludes with an analysis of some of the problems of the kind of liberalism espoused by Mill’s Liberty Principle.