1 The Professional Association of Diving Instructors (PADI) is the world's largest recreational diving membership and diver training organization founded in 1966 by John Cronin and Ralph Erickson. Cronin was originally a NAUI instructor who decided to form his own organization with Erickson, and to break diver training down into different courses instead of the single universal course then prevalent.

PADI courses range from entry levels (such as "Scuba Diver" and "Open Water Diver") to "Master Scuba Diver" and a range of instructor certifications. Via their affiliate, Diving Science and Technology (DSAT), they also offer various technical diving courses, including decompression diving, trimix diving and gas blending.

The PADI system is composed of modules with standardized learning objectives divided into theory and practical skills development. Theory is mainly conveyed by way of self-study using books, computer based training using CD-ROM or online learning. All study options are supplemented with video to help the student diver visualize what they have read. Confirmation of the student diver's level of mastery in standardized knowledge review sessions is carried out by a scuba instructor. Practical skills mastery is obtained through confined water training (pools or relatively shallow water) and performance evaluations in open water. Upon completion of each course, a certification is issued to the student.

PADI courses are performance based dive programs, and at the introductory level emphasize practical knowledge, safety and motor skills. The foundations of diving physics, physiology and chemistry are built during entry level programs. The more esoteric details of these concepts are left for later courses when the diver has gained practical knowledge and experience beyond the entry level. These practices fall within current modern learning philosophies and receive regular updates via peer review.

PADI is a member of the World Recreational Scuba Training Council. 2 Today PADI issues approximately 950,000 certifications a year, of which approximately 550,000 are entry level certifications. Over the years since its formation PADI has become a prominent provider of scuba diver training; an online extract of the 2007 edition of Frommer's Portable Aruba indicated that "70% of divers in the United States and approximately 55% of divers worldwide" were certified by PADI.

Research by Leisure Trends for the Diving Equipment and Marketing Association shows that in 1999 almost 60% of retailers in the US issued PADI certificates, while NAUI and SSI certificates were issued by about 20% each. Unfortunately there is currently no centralised source of accurate industry-wide information regarding the combined number of certifications issued by all the certifying agencies within the recreational diving industry. In the absence of a reliable source of independent industry-wide data, the above statement should be viewed as an estimate only and should not be relied upon as being evidence of PADI's current level of representation within the dive industry.