Domestic law, case law and policies play a decisive yet underestimated role in ensuring that partnered operations are carried out in compliance with international law. Research on the legal framework of partnered operations has so far focused on clarifying existing and emerging obligations at the international level. Less attention has been devoted to understanding whether and how domestic legal systems integrate international law into national decision-making which governs the planning, execution and assessment of partnered operations. This article tries to fill the gap by focusing on the practice of selected States (the United States, the United Kingdom, Denmark, Germany and Italy), chosen for their recent or current involvement in partnered operations. By using the International Committee of the Red Cross's “support relationships” framework and based on a comparative analysis of practice, the study seeks to evaluate the effectiveness of national laws, case law and policies according to their ability to prevent or mitigate the risk of humanitarian consequences posed by partnered warfare.