Green roofs are roofs covered with vegetation and are considered a nature-based climate solution. Extensive green roofs use hardy plants and require little maintenance, while intensive green roofs resemble gardens or parks and require more maintenance. Green roofs cool their buildings and the surrounding environment through absorption of solar radiation and evapotranspiration. They benefit health by reducing the temperature of indoor environments; they can also reduce air pollution and improve mental health through nature contact. There are no studies that have directly observed impacts of green roofs on health care utilization or mortality. In simulations, widespread green roof adoption reduced indoor air temperatures 2-3°C (3-5°F), reduced population-weighted summertime temperature by 0.35°C (0.63°F), and reduced heat-related mortality by 0.21%. Green roofs are more expensive than conventional roofs to install and maintain but last about twice as long, yielding a small net cost premium that is considered marginal over the roof’s lifetime. Alternatives to green roofs include high albedo (highly reflective) roofs, though these roofs also retain less solar radiation in winter, resulting in higher heating costs.