The closed circuit rebreather (CCR) is not a new diving technology. From the late 1990s CCR units were commercially available in Europe, and increasingly more divers, and among them scientific divers, have been trained to use them. Even if many benefits exist for using CCR for all diving depth ranges, it is in the deep diving zone ranging from 50 m to 100 m of sea water where the main advantages to using this equipment exist. Using rebreathers does carry additional risks, and these must be mitigated to ensure safe usage. A standard for CCR scientific diving has existed for many years in the USA, and the levels of expertise within the European scientific diving community are now sufficient for a European standard to be established. National legislation for occupational scientific diving in many cases excludes CCR diving, which can limit its use for scientific purposes. This paper suggests that, where possible, legislations should be allowed to evolve in order to include this type of equipment where and when its use has direct advantages for both the safety and the efficiency of scientific diving. This paper provides a brief description of the fundamentals of closed circuit rebreather diving and outlines the benefits that its use offers diving scientists. Special attention is given to safety issues with the assertion that the CCR concept is, if strictly applied, the safest available technique today for autonomous deep scientific diving purposes.