The concept that certain objects and persons may be legitimately attacked during armed conflicts has been well recognised and developed through the history of warfare. This book explores the relationship between international law and targeting practice in determining whether an object is a lawful military target. By examining both the interpretation and its post-ratification application this book provides a comprehensive analysis of the definition of military objective adopted in 1977 Additional Protocol I to the four 1949 Geneva Conventions and its use in practice.