The workshop "How can an international pandemic instrument address One Health" sought to familiarize members of Geneva-based permanent missions and government officials from capitals with the legal and institutional aspects of "One Health" in the context of negotiations of a future international instrument on pandemic prevention, preparedness, and response ("pandemic instrument").1 The workshop identified legal and scientific challenges for implementation of One Health. The presenters identified a regulatory "blind spot" at the midstream level of prevention: the measures contained in the International Health Regulations 2005 (IHR) focus on detecting and containing the international spread of a communicable disease once it occurs, but do not provide a strategy for deep prevention of zoonotic diseases. Specific measures, involving integrated surveillance, regulatory obligations, science-policy interfaces and coordination mechanisms were proposed to address that regulatory gap. The workshop emphasized the complexity of One Health and the importance of addressing the human-animalenvironmental health nexus in an integrated, multi-sectoral manner. The workshop participants agreed on the importance of continuing the discussions concerning the way of addressing One Health in the new pandemic instrument.