This book tackles the enduring puzzle of consent-based use of force in international law. Why can force be justified by state consent, and under what conditions is such justification valid? These questions have long been treated separately. This study brings them together through a new theoretical framework that connects theory and practice. Drawing on the humanisation of international law, it reconstructs the principle of non-use of force by integrating a human-centred perspective into the traditional state-to-state model. By doing so, it offers a coherent account of consent-based force and redefines the role of human interests within a fundamentally state-centric legal order.