Rebreather diving systems have many advantages to standard open-circuit systems (or SCUBA). Rebreathers offer higher gas efficiency together with silent and bubble-free diving. Moreover, instead of cold and dry gas found in open-circuit systems the diver takes advantage of a warm and humid breathing gas. Stealth (through silent, bubble-free diving) can be beneficial for scientists exploring a range of natural ecological research areas. The high gas efficiency of rebreathers, combined with their lower operational costs, can provide longer autonomy and shortened decompression obligations that may assist the scientist with deeper diving explorations. The present paper gives an overview of today's rebreather technology and focuses especially on the needs of scientific divers. Moreover, it includes a short report about achievements in the field of deep coral explorations, where advanced electronically-controlled closed-loop rebreather systems were the key for efficient and successful missions.