This article reflects on the proliferation of responses to the so-called phenomenon of “foreign terrorist fighters,” and the profound human rights challenges they give rise to. It considers national, regional and international developments, many spurred by an activist Security Council, through which expanded powers have been assumed and rights restricted by reference to the need to respond to ftf threats. A series of uncomfortable relationships emerge from this analysis. They include for example tensions: between the evolving and still relatively superficial understanding of the nature and source of uncertain threats and contributing factors on the one hand, and the onerous and far-reaching nature of responses directed against them on the other; between the expansive use of coercive measures including criminal law, and basic constraining principles of criminal law upon which its legitimacy and power depends, such as individual culpability, harm principle and remoteness; or between the original purposes of most ftf measures and their impact in practice, on the operation of humanitarian law, on humanitarian workers and human rights defenders, and on the rule of law. Exceptional ftf measures continue to spread their reach and creep into other areas of security and organised crime. The article highlights the need to consider the short and long term impact, on the full range of rights of many, of the array of administrative, criminal and other measures being passed into law and implemented in practice across the globe in the name of responding to the ill-defined phenomenon of “ftfs”.