This case study, Promoting Multisectoral Collaboration for Resilient Health Systems Through One Health Platforms: Lessons from Ethiopia, Liberia, Nigeria, and Zambia, highlights how Breakthrough ACTION used multisectoral collaboration to strengthen health systems against zoonotic diseases and emerging threats. Intended for health professionals and policymakers, it demonstrates the value of integrating human, animal, and environmental health efforts. The case study provides actionable insights and recommendations for other countries, emphasizing the importance of joint training, community engagement, and coordinated response mechanisms to build resilient health systems and enhance global health security.