© 2020 by Nova Science Publishers, Inc. All rights reserved. The European principle of ne bis in idem is a universally recognised legal doctrine and fundamental right that prohibits the repetition of criminal proceedings against the same defendant for the same criminal offence. The principle is known as the rule against double jeopardy in common law jurisdictions. This chapter aims to critique the substance, scope, and interpretation of the European ne bis in idem principle as an autonomous procedural defiance. To this end, an assessment of the principle as provided for in European treaties and conventions and concomitant jurisprudence from international courts and tribunals will be examined to identify emerging themes and guidelines.