Professional Diving is a type of diving where the divers are paid for their work. There are several branches of professional diving, the most well known of which is probably commercial diving. Any person wishing to become a professional diver normally requires specific training that satisfies legislation, such as that set by the United Kingdom Health and Safety Executive. Due to the dangerous nature of some professional diving disciplines, specialized equipment such as a diver to surface communication system is often required by law.

Commercial diving:

HAZMAT diving is widely regarded as the most dangerous branch of the commercial diving industry, employing highly skilled and experienced staff. Typical work involves diving into raw sewage or dangerous chemicals, such as paper pulp, liquid cement, or oil sludge. This causes special requirements:

•  The divers need to be vaccinated against diseases such as hepatitis and tetanus.
•  The dive company needs to have specialist plans in place for decontamination of the diver and equipment after a dive.
•  A way to recover the diver if something goes wrong.
•  The diver's weighting may need to be adjusted, if he is diving in a liquid whose density is much different from the density of water.

The main tasks a diver can be found to be doing include:

•  Essential maintenance of underwater valves and sluice gates.
•  Repairing damaged pipelines.
•  Pollution control work to contain, control, and clean up after a pollution incident.
•  Some divers are required to dive into landfill sites to maintain the pumping equipment, vital in preventing landfill sites from filling up --with rainwater and contaminating the water table.
•  Welding inside live sewers or working in septic tanks.
•  Miscellaneous repairs and finding lost objects.
•  Finding bodies.

Sewer diving is often considered the most dangerous of all the HAZMAT jobs due to the diseases contained in raw sewage and because syringes and glass find their way into the raw sewage, creating risks of contracting diseases. Divers working in an environment harmful to their health will always wear a full drysuit with thick gloves which are attached directly to the suit, the helmet and boots will also attach directly to the drysuit, this allows the gloves, boots, suit and helmet to be pressured in order to prevent ingress of liquid should a puncture occur. Normally, to achieve this, a diver will use a free flow diving helmet which continually supplies enough air for the diver to breathe plus an additional amount to pressurise the suit; a free flow helmet has a much lower chance of leakage through the exhaust valve compared with a demand helmet where the exhaust valve is dormant during the inhalation stage of the diver breathing. The drysuit will be made from a material resistant to whatever hazard the diver faces: normally the diver wears a vulcanised rubber drysuit, but occasionally a neoprene or tri-laminate suit is needed. Often, a diver will wear extra protection over their drysuit to decrease the chance of a puncture: leather, PVC, and nylon coveralls are used for this purpose. In such diving light is often very scarce, so most such divers rely on touch to guide them, and are usually connected via rope to the surface.

Police divers are normally police officers or firefighters, who have been trained in the use of diving techniques to recover evidence and occasionally bodies from rivers, canals and the sea. They may also be employed in searching shipping for contraband substances fitted to the outside of hulls to avoid detection. The equipment they use depends on requirements, but the requirement for communications at some sites does often require the use of full-face masks with communication equipment, either with SCUBA or surface supplied equipment.