This Big Catch-Up Progress Newsletter serves as a global overview of the implementation of the BCU initiative across 36 countries. It aims to provide a data-driven summary of progress made in reaching zero-dose and under-immunized children with catch-up vaccine doses, while strengthening routine immunization systems. The newsletter report is a strategic governance tool to share BCU programme updates and insights, highlight achievements and challenges, as well as offer a platform to distill lessons learned, document implementation progress, and share country-driven innovations; in a bid to support informed decision-making, strategic improvements and provide a valuable understanding to improve coordination, and enhance the effectiveness of the BCU initiative. By sharing these report insights, we aim to foster cross-country / regional learnings and reinforce collective accountability for reaching every missed child.