Free speech is an essential feature of liberal democracies, as it allows for different views and opinions to be expressed. However, proclamations based on corrupt assumptions can lead to horrible events. Because of this, speech can legitimately be limited. This work provides operational guidelines on how to do so while complying with human rights fra-meworks and with the rule of law in the specific case of incitement to terrorism. On the matter, which is gaining increasing academic attention, opposed opinions and contrasting practices remain. The core issue is: where should the line be crossed between praise, the legitimate expression of a controversial opinion, and peril, an act of speech that creates a real threat of harm? This issue is tackled here from the perspective of international law. Firstly, incitement to terrorism is defined by considering the key elements of this crime separately. Secondly, the legal regime of protection of freedom of speech is looked at to determine whether incitement to terrorism can legitimately be prohibited. Finally, the question of whether criminal law, and especially inchoate offences, constitute an appro-priate tool for prevention is asked. An answer is provided here by establishing a distinc-tion between preventive and pre-emptive measures based on the criteria of threat speci-ficity, short time horizon and imminence of harm. Based on this distinction, only pre-emp-tive prohibitions to incitement to terrorism are considered admissible.