The criminal law frameworks of countries that have been the subject of international peacekeeping operations and military interventions often reveal an urgent requirement for reform. Destabilised by conflict, existing frameworks may be discriminatory and inconsistent with international human rights and due process standards. New law may be imperative to promote the development of fair and effective justice systems, rule of law and transitions from conflict to peace. While the transplantation of readily-available law can be an appealing solution a fundamental concern for legislators is whether it represents a reasonable and effective mechanism for developing vital post-intervention criminal law reform. This thesis addresses this issue by examining the Interim Criminal Procedure Code 2004 and the Counter Narcotics Law 2005, two laws developed by legal transplantation in Afghanistan, the most recent example of a country where the international community is engaged in post-intervention criminal law reform. It does this by firstly developing a new evaluative test developed from an examination of theoretical perspectives on transplant feasibility. It then applies this test using quantitative data supported by original qualitative research from interviews with senior Afghan and international legal personnel. It finds that neither law has been successful. Their transplanted content and the processes of transplantation have reduced the extent to which they have been accepted and achieved their objectives and have increased their potential to be ‘lethal' transplants capable of promoting injustices, generating destabilising discontent and moderating rule of law promotion. This study questions the assumption that it should always be reasonable to develop post-intervention criminal law by means of legal transplantation. The reasonableness of relying on legal transplantation will depend on the sensitivity with which it is employed, requiring knowledge of legal transplant feasibility, local history and legal traditions and the prior application of the proposed evaluative test to assess potential receptivity.