For the past 40 years, Iliffe has conducted studies of biodiversity, ecology, evolution, and conservation of animals inhabiting saltwater caves. In addition to his extensive cave investigations in Bermuda, he has led biospeleological research expeditions to the Bahamas, Belize, Mexico, Jamaica, Dominican Republic, Canary Islands, Iceland, Mallorca, Romania, former Czechoslovakia, Gal?pagos, Hawaii, and numerous locations in the Indo-Pacific. This research has resulted in the discovery of more than 300 new species of marine animals, mostly crustaceans, inhabiting caves in the Atlantic, Caribbean, and Indo-Pacific. Iliffe's research has been funded by grants from the National Science Foundation, National Oceanic and Atmospheric Administration, and the National Geographic Society, among others. He has published 250 papers, including 30 invited book chapters. TV documentaries featuring his cave diving research expeditions can be seen on the National Geographic Channel, BBC, PBS, History Channel, Discovery Channel, and others.