COVID-19 is the most significant public health emergency in more than a century, caused a global economic crisis, and has long-term repercussions across society. This unprecedented crisis has highlighted the urgent need for smart investments to strengthen health system resilience. There is a need to protect people’s underlying health; fortify the foundations of health systems; and bolster health professionals working on the frontline. This report identifies a set of priority investment areas needed to strengthen health system resilience. It then produces order-of-magnitude estimates of the expected costs of such investments, drawing extensively from existing OECD data and analytical studies. These priority investments represent an estimated 1.4% of GDP, on average across OECD countries (and ranging from 0.6-2.5%), as compared with pre-pandemic expenditure of 8.8%. A combination of targeted spending and measures to reduce wasteful spending could mitigate the overall increases in health spending in the medium to long term.