There are a number of institutes which offer certifications for those who wish to become regular divers. When choosing an institute make sure that you are comfortable with their global recognition, ISO certifications and the level of knowledge of the instructors. There are many different certifications available including: Discover Scuba Diving, Open Water Diving, Adventure Diving, Rescue Diving and quite a few others. The more advanced certifications will always require you to have at least one prerequisite certification. All the information for these certifications is available on the individual websites of the institutions.
PADI: Professional Association of Underwater Instructors
IANTD: International Association of Nitrox and Technical Divers
NAUI: National Association of Underwater Instructors
PSAI: Professional Scuba Association International
SSAI: Scuba Schools International
UTD: Unified Team Diving
Medicine and Physiology
Medical advice for divers is available from Ernest S. Campbell, MD, FCAS, a former surgeon and diver, at Diving Medical Online
Divers Alert Network - A guide to health and fitness for scuba divers by the director of medical services.
Undercurrent - Diving health and safety articles with unique information on drug use and its effects on diving, and even shark bites.
Divers Alert Network - The safety organisation for divers.