The basic issue that this chapter examines is how we set morally justifiable limits on what people say online, with a specific focus on speech acts related to terrorism. The chapter takes as one of its foundational assumptions that there are situations in which free speech, while an important and potentially fundamental right, can be justifiably limited: ‘If there is a Free Speech Principle, it means that free speech is a good card to hold. It does not mean that free speech is the ace of trumps’. This chapter draws from discussions of free speech to explain how and when particular sorts of constraints on public
communications are justified. It begins with a recognition that the norms of behaviour and free speech online are evolving, moves to an exploration of the key conceptual and ethical discussions around free speech, and closes with a set of framing questions to give some guidance as to how we can approach the question of whether online terrorist public communications should be restricted or not.