Free speech is a widely held principle. This is in some ways surprising, since formal and informal censorship of speech is widespread, and rather different issues seem to arise depending on whether the censorship concerns who speaks, what content is spoken or how it is spoken. I argue that despite these facts, free speech can indeed be seen as a unitary principle. On my analysis, the core of the free speech principle is the denial of the denial of speech, whether to a speaker, to a proposition, or to a mode of expression. Underlying free speech is the principle of freedom of association, according to which speech is both a precondition of future association (e.g. as a medium for negotiation) and a mode of association in its own right. I conclude by applying this account briefly to two contentious issues: hate speech and pornography.