This document outlines HAI's model of health systems strengthening which focuses on working with public sector institutional health systems. It discusses the importance of strong public health systems for scalability, equity, and specialized services. HAI works in key areas like integrating services, leadership and management, health systems research, and community linkages. Examples from Timor-Leste and Côte d'Ivoire show HAI's work improving maternal and child health services, developing health facilities, training health workers, and strengthening community outreach. The document concludes by discussing opportunities to further strengthen whole health systems through integrated services, workforce issues, information systems, and leadership coordination.