This thesis examines the purpose and function of international law on torture from both a normative and legal perspective. It seeks to re-examine the scope, justifiability and purpose underlying the current international prohibition of torture from both a philosophical and legal point of view, and do so in light of recent state counter-terrorism efforts. The thesis begins by setting out a historical narrative of the development of the prohibition on torture versus the state practice of ill-treatment, describing the gap that has persistently existed between law and practice since the widespread European abolition of torture. The thesis then goes on to examine the moral dimensions of a prohibition on torture and to ask whether prohibiting torture is always morally desirable. From there, the thesis engages with the issue of whether or not torture should be legalised in certain circumstances, so as to avoid the charge of hypocrisy that some scholars claim exists when a prohibition of torture is maintained despite the gap between the law on torture and state practice of torture. The thesis finds that ultimately, while there are conceivable situations in which torture may be morally necessary, and while it is possible to construct a law that would regulate the use of torture in a manner that is more transparent and accountable, that the risks in institutionalising torture are too substantial to implement such a law safely. However, the thesis argues that the charge of hypocrisy can be avoided and the gap between law and practice minimised by improving the structural elements of the current prohibition, in particular its definition of torture and the ways in which states adopt the prohibition domestically.