Learn how scuba diving works, before the first breath.

Read these pages in order if you are starting from zero. They explain how diving is organised, not how to dive: skills, dive planning and emergency procedures are taught by an instructor in a course from a recognised agency, and no page on this site replaces that. When you are ready for more, the equipment section explains what the gear does and which standards apply to it, the safety section sets out what diving medicine and safety bodies publish, and the glossary explains the vocabulary.

The shortest possible version

• Scuba stands for self-contained underwater breathing apparatus: the diver carries the breathing gas, with no supply from the surface (Wikipedia, secondary).
• Training and certification come from agencies, clubs and federations such as PADI, SSI, NAUI, BSAC, CMAS, SDI, GUE and RAID. Shops, boats and resorts may ask to see a certification card before they rent gear, fill a cylinder or take someone diving (Wikipedia, secondary).
• The international standard ISO 24801 separates supervised divers (Level 1) from autonomous divers (Level 2), who are qualified to dive without a dive professional, and dive leaders (Level 3).
• There is no single depth limit. Each agency publishes its own for each card: PADI lists 18 m (60 ft) for Open Water Divers (27 February 2024), BSAC lists 20 m for Ocean Divers, and GUE lists 21 m (70 ft) for its Open Water Divers (both on undated course pages). SSI, in an undated article, calls 40 m (130 ft) the generally accepted maximum recreational depth.
• Agencies and clubs use medical screening forms before training. Under the 2020 questionnaire, as PADI describes it, a yes answer can mean a physician must approve diving; in the UK club system, a yes means contacting a UKDMC Medical Referee.

Who sets the rules?

Diving has no single rulebook. Each agency writes its own courses and limits, regional training councils under the World Recreational Scuba Training Council publish shared minimum training standards, and ISO standards describe what a diver at each level must be able to do. So every page in this section names the body whose statement it is quoting, with a date where the body gives one. Where sources disagree, both versions are given.

Where to go next

Start with how scuba diving works and why certification matters. To compare agencies and cards, read training agencies, certification levels and depth limits by certification. If you are thinking about a first course, try diving, medical screening and getting started set out what the agencies publish about each step.