The Top 3 Scuba Certification Agencies:
Professional Association of Diving Instructors (PADI)The most commonly heard of, PADI courses are dive programs that are performance-based. Introductory level of PADI emphasises practical knowledge, motor skills and safety, plus the foundations of diving physics, physiology, and even chemistry. PADI centers are currently the most widely spread out across the world, you can find one at literally any dive destination. There are more beginner divers are certified by PADI than all other agencies combined. It has certified about 55% of divers worldwide!
National Association of Underwater Instructors (NAUI)Its diver courses are very similar to those conducted by PADI, and it enjoys the status of being the second largest scuba certification agency in the world.
Scuba Schools International (SSI)What differs SSI from other diver education organizations (PADI, NAUI, CMAS etc) is that SSI is a retail-based organization that intends to ensure the quality of training around the world. While SSI themselves also teach basic theories through their academic sessions online before placing them in real practice with monitored scuba diving trainings in confined water/pools. If you’d like to complete this course, you will have to go on at least 4 open water adventure dives to achieve SSI’s Open Water Diving Certification.