Most diving takes place in what is called the recreational range. This is any dive shallower than 40 meters. For most of these dives, they take place in 25 meter or less. Try dives and first few dives of training is usually limited to 12 meters. Entry level certification are limited to 18 – 20 meters depending on the agency. More advanced divers are trained to dive to up to 30 meters. And with special training recreational divers can reach depths up to 40 meters.
Divers going over this limit need some special training and equipment. It is then called extended or technical diving and is a lot more demanding. This kind of diving has also a lot more risks. Currently the deepest dive has been done by Amer Gabr in the Red Sea in Egypt at a depth of 338 meters.