This volume of the Yearbook of International Humanitarian Law takes a close look at the role of so-called “expert manuals” in the interpretation and development of the international law of armed conflict and connected branches of international law relating to military operations. While these manuals can and do play an undoubtedly useful role, their proliferation raises a number of questions. What degree of authority do they have and how much weight should be given to the views expressed in them? What is the methodology they employ and how effective is it in ensuring an as objective and impartial interpretation of the law as possible? What is their place in the doctrine of sources? While there is already a considerable body of literature addressing these and other relevant questions, this volume aims to contribute further to this discussion with contributions by three experts involved in one or more of these manuals in one capacity or another.