Over recent decades, international humanitarian law has been shaped by the omnipresence of so-called expert manuals. Astute and engaging, this discerning book provides a comprehensive account of these black letter rules and commentaries produced by private expert groups and demonstrates why the general acceptance of these expert manuals is largely unjustified. The author innovatively links interdisciplinary insights to the needs of military lawyers in practice, showing the pitfalls of relying on private manuals as arguable restatements and interpretations of the law 'as it is'.