This article considers the moral limits to national security policies. While it may seem self-evident that there are, and ought to be, limits to counterterrorism policies, there is an increasingly widespread public opinion that political leaders can, and must, do everything they can to protect against terrorist acts. Liberal-democratic societies are facing the threat of domestic terrorism, and for a political leader to say that 'we cannot stop all terrorist acts and, indeed, neither should we' would sound the death knell for their career. This article seeks to specify the limiting conditions around counterterrorism policy by reference to policymakers' public justifications offered for counterterrorism policy. This article presents three normative elements that underpin counterterrorism policy to show that there are important reasons to limit counterterrorism policy, and to suggest that these limits ought to be recognised by political leaders and citizens alike in liberal-democratic societies. Having set out three limiting factors on counterterrorism policy, the article then shows that these factors do indeed play a role in UK counterterrorism policy development—that is, in recognising the justificatory apparatus for national security policies, limiting conditions ought to be found that are sensible to, and accepted by, the proponents of such policies.