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. 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.