That certification is more than just a Blockbuster card. Diving offers an amazing experience and one that should be prepared for carefully -- the sense of darkness, enclosure, and not-exactly-silence can trigger anxiety in even the most adventurous. And the effects of pressure on the body are important to understand, as is the mathematics for correctly using the dive tables. The equipment itself must also be thoroughly familiar to the diver. The proper use of your equipment should be second nature, so you're ready for surprises -- and enjoying the astonishing beauty and strangeness of the underwater world.
A Blend of Education and Sales
Dive shops offer many services: certification classes, filling tanks with air, renting and selling equipment, and advice about local spots and weather conditions. But they aren't just in it to put a smile on your face. The same centers also sell equipment and continuing education, and they want to keep you coming in for both. Dive shops often sell tours as well, offering a chance to explore even if you don't have a regular dive partner or don't feel comfortable venturing out without a divemaster.
The Major Certification Agencies
The largest dive-certification organization is PADI, the Professional Association of Diving Instructors. PADI boasts a gigantic worldwide network of affiliated dealers and claims to certify almost a million divers a year. PADI even has a diver's insurance program, to cover treatment of diving accident or injury. PADI offers other services and is the organization you are most likely to encounter at resort spots, typically offering short courses that get the vacationer into the water fast.
Other certification bodies include SSI (Scuba Schools International) and NAUI (National Association of Underwater Instructors). Their affiliates may be slightly harder to find, but they have a high standard of education, and they participate with several other certifying organizations in a "Universal Referral Program" that allows a diver to take classroom and pool instruction at one place (maybe near home, in some cold-water or land-locked place) and open-water testing with any affiliate (say, in Belize or Mexico). These programs may not offer their own diver's insurance, but DAN (Divers Alert Network) is available for that. They also have or are affiliated with large worldwide networks of dealers.
Shops often affiliate with more than one of these certifying organizations, even if they offer classes through only one. So Joe's Local Dive Hut may offer classes taught by SSI instructors, but it probably has a PADI affiliation and will welcome your PADI-issued C card when you come in to rent gear or get air.
