The COVID-19 pandemic has made vivid the need for resilient, high-quality health systems and presents an opportunity to reconsider how to build such systems. Although even well resourced, well performing health systems have struggled at various points to cope with surges of COVID-19, experience suggests that establishing health system foundations based on clear aims, adequate resources, and effective constraints and incentives is crucial for consistent provision of high-quality care, and that these cannot be replaced by piecemeal quality improvement interventions. We identify four mutually reinforcing structural investments that could transform health system performance in resource-constrained countries: revamping health provider education, redesigning platforms for care delivery, instituting strategic purchasing and management strategies, and developing patient-level data systems. Countries should seize the political and moral energy provided by the COVID-19 pandemic to build health systems fit for the future.