This public-health infrastructure guide from Grantmakers in Health explains how philanthropic funders and public-sector partners can build and strengthen public-private partnerships to support and improve U.S. public health infrastructure. It highlights lessons from foundation collaborations with health departments—such as flexible funding, coordinated strategies, data partnerships, multisector coalitions, and long-term commitment—to boost public health capacity, equity, and resilience, especially in light of challenges revealed by COVID-19.