The tropics are home to a dizzying array of species, store vast quantities of carbon, drive year-to-year climate variability, and will soon be home to half of the world’s population. In this Insight, we explore some of the scientific and societal challenges posed by the tropics, and some of the solutions being devised. Mosquito-borne diseases, such as dengue and malaria, are a major cause of morbidity in the tropics.