The urban heat island effect is a major sustainability challenge for cities. Trees or large greenspaces are effective at reducing local temperatures, but in densely built areas, green roofs are often encouraged as an alternative. This potential for urban heat island mitigation is a strong motivator for integration of green roofs into planning and policy. However, research that rigorously assesses cooling effects of green roofs is lacking relative to other types of green infrastructure. We will share results of a meta-analysis assessing the magnitude of temperature reduction provided by green roofs, including factors that contribute (or detract) from their success.