Scientific diving is the use of underwater diving techniques by scientists to perform work underwater in the direct pursuit of scientific knowledge. The legal definition of scientific diving varies by jurisdiction. Scientific divers are normally qualified scientists first and divers second, who use diving equipment and techniques as their way to get to the location of their fieldwork. The direct observation and manipulation of marine habitats afforded to scuba-equipped scientists have transformed the marine sciences generally, and marine biology and marine chemistry in particular. Underwater archeology and geology are other examples of sciences pursued underwater. Some scientific diving is carried out by universities in support of undergraduate or postgraduate research programs, and government bodies such as the United States Environmental Protection Agency and the UK Environment Agency carry out scientific diving to recover samples of water, marine organisms and sea, lake or riverbed material to examine for signs of pollution.

Equipment used varies widely in this field, and is generally selected based on cost, effectiveness, availability and risk factors. Open-circuit scuba is most often used as it is widely available and cost-effective, and is the entry-level training mode in most places, but since the late 1990s the use of rebreather equipment has opened up previously inaccessible regions and allowed more reliable observations of animal behaviour.

Scientific diving in the course of employment may be regulated by occupational safety legislation, or may be exempted as self-regulated by a recognised body. The safety record has generally been good. Collection of scientific data by volunteers outside of employment is generally considered to legally be recreational diving.

Training standards vary throughout the world, and are generally higher than for entry level recreational diving, and in some cases identical to commercial diver training. There are a few international agreements that facilitate scientists from different places working together on projects of common interest, by recognising mutually acceptable minimum levels of competence.

Scientific diving is any diving undertaken in the support of science, so activities are widely varied and may include visual counts and measurements of organisms in situ, collection of samples, surveys, photography, videography, video mosaicing, benthic coring, coral coring, placement, maintenance and retrieval of scientific equipment.

The importance of diving to the scientific community is not well recorded. A bibliographic analysis of papers published between 1995 and 2006 that have been supported by scientific diving shows that diving supports scientific research through efficient and targeted sampling. Activities include collection of organisms and biological samples, observing animal behaviour, quantitative surveys, in situ measurements, impact studies, ecological analyses, evaluation of techniques, mapping underwater areas, profiling geology, and deploying and retrieving underwater equipment.

A comparison of database searches against a selection of publications known to have used scientific diving in the same period, shows that a small minority of papers were discovered, suggesting that the importance of scientific diving as a valid and cost-effective underwater research tool is greatly underrepresented in the literature.

Some underwater work in support of science is out of scope of the relevant regulations, exemptions, or codes of practice, and is not legally classed as scientific diving. This work is required to be done by divers trained, registered, and operating following commercial diving health and safety practices.