Prosecution of serious crimes of international concern has been few and far between before and even after the establishment of the International Criminal Court in 2002. Hope thus rests with the implementation of the international legal obligation for States to either extradite or prosecute such perpetrators among themselves or surrender them to a competent international criminal court. This obligation was considered by the United Nations International Law Commission (ILC) which submitted its final report in 2014. Kittichaisaree, Chairman of the ILC Working Group on that topic, not only provides a guide to the final report, offering an analysis of the subject and a unique summary of its drafting history, he also covers important issues left unanswered by the report, including the customary international legal status of the obligation, the role of the universal jurisdiction, immunities of State officials, and impediments to the surrender of offenders to international criminal courts. Authoritative, encyclopaedic, and essential to those in the field, The Obligation to Extradite or Prosecute also offers practical solutions as to the road ahead.