As the climate changes, hotter-than-usual days and nights are becoming more common, and heat waves are expected to become more frequent and intense. Cities experience higher temperatures than surrounding areas–known as the urban heat island effect–and residents often face higher health risks during extreme heat events. To help monitor changes in the health challenges associated with heat waves in urban areas, the USGS and EPA are developing data, analyses, and indicators for characterizing trends in the urban heat island effect. Integration of long-term USGS–NASA Landsat surface temperature data and annual land cover change information from the 1980s to the present is allowing for new ways to study changes in urban heat island intensity across U.S. cities and beyond. Data are available for 50 U.S. cities and surrounding areas.