In 2005, months of unprecedented higher-than-normal water temperatures started a cascade of bleaching, disease, and death among corals in the Eastern Caribbean. Such events are increasing in frequency around the world and threaten these fragile ecosystems, which shelter a wealth of biodiversity and provide sources of food and pharmaceuticals. Researchers must determine how rising temperatures produce coral bleaching, the pathogens that cause disease in corals, and the environmental factors that foster disease outbreaks.