Diadematids form a prominent component of shallow water reef communities, living predominantly in the more sheltered backreef and peri-reefal environments. They are epifaunal and can be found out in the open during the day, relying on herding and their long spines for protection. Their diet comprises small benthic organisms scraped off hard substrates or picked up from the sea-floor. Most species live in shallow water settings of less than 40 m, but a few occur in deeper water shelf settings to about 400 m.
Species whose larval development is known are all planktotrophs. Their larvae has a highly characteristic form with just two elongate arms.