This work investigates the precise methodology required to identify and verify rules of customary international law within the global legal framework. The author, Sir Michael Wood, leverages his extensive experience as a former Special Rapporteur for the International Law Commission to provide a rigorous analysis of state practice and opinio juris. By synthesizing historical precedents, judicial decisions, and scholarly commentary, the text establishes a structured approach for practitioners and academics to navigate the complexities of international legal formation.

Legal scholars and practitioners frequently cite this text as a definitive reference for understanding the evidentiary standards of international law. Experts highlight the clarity of the prose and the author's ability to distill complex procedural questions into a coherent framework for application.