A Master Instructor in scuba diving

Scuba diving

Scuba diving is a form of underwater diving in which a diver uses a scuba set to breathe underwater....

 is one of the highest levels of professional training in North American based diver training organizations, usually only one step below Course Director for the Instructor Development Course (IDC).

The requirements for the Master Instructor rating vary according to organisation.

PADI

The requirements for an individual to become a PADI

Professional Association of Diving Instructors

The Professional Association of Diving Instructors is the world's largest recreational diving membership and diver training organization founded in 1966 by John Cronin and Ralph Erickson...

 Master Instructor are:

1. Has renewed, teaching status as an IDC Staff Instructor.
2. Has been a PADI Open Water Scuba Instructor for at least two years.
3. Is an Emergency First Response Instructor.
4. Has certified at least 150 PADI divers, of which:
   1. At least 50 of the certifications must be for PADI Adventure Diver or higher
      Advanced Open Water Diver
      Advanced Open Water Diver is a scuba diving certification level provided by several diver training agencies, such as Professional Association of Diving Instructors , Scuba Schools International and Underwater Explorers' Federation...
      
      .
   2. At least 15 of the certifications for PADI Specialty Diver.
   3. At least 5 of the certifications for PADI Rescue Diver
      Rescue Diver
      Rescue Diver is a scuba diving certification level provided by several diver training agencies, such as PADI, SSI, SDI, and NAUI, which emphasises emergency response and diver rescue....
      
      .
   4. At least 5 for PADI Divemaster
      Divemaster
      A Divemaster is a diving qualification used throughout most of the world in scuba diving for a diver who has overall responsibility for a group of divers...
      
      .
   5. At least 5 for PADI Assistant Instructor.
   6. No more than 75 of the 150 certifications may be from credits earned for conducting Discover Scuba Diving (DSD) experiences.
   7. No more than 50 of the 150 certifications may be from credits earned for staffing IDCs.
   8. No more than 25 of the 150 certifications may be from non-diving specialty certifications. (i.e. Equipment Specialist, Project AWARE Specialist, etc.).
   9. No more than 10 of the 150 certifications may be from PADI Seal Team or Master Seal Team registrations.
   10. At least 10 students through the Emergency First Response program.
5. Possesses a complete understanding of the PADI System of diver education.
6. Has participated in at least three PADI Instructor Development Seminars.
7. Uses the complete PADI System of diver education including all appropriate PADI training materials when conducting PADI programs.
8. Issues PADI as the primary certification, and conduct all PADI certification courses and experience programs using methods consistent with PADI Standards and philosophy as outlined in the PADI Instructor Manual.
9. Has no verified Quality Assurance violations within the previous six months and no open quality assurance inquiries in progress. (A member in review status may not qualify for Master Instructor until the Review status is lifted.)
10. Demonstrates support of the PADI organization in its efforts to establish programs in aquatic education and conservation.

SSI

SSI

Scuba Schools International

Scuba Schools International or SSI is an organization that teaches the skills involved in scuba diving and supports Dive Businesses and Dive Resorts.SSI has well over 2,500 authorized dealers and 35 Regional Centers and Area Offices all over the World....

 provides several different ways to reach the Master Instructor rating, whereby different candidates can "compensate" for lesser achievements in some requirements (eg. number of logged dives) if they have stronger achievements in other areas (number of SSI certifications).

Option 1:

• Be currently certified as an Advanced Open Water Instructor
• Have at least 4 years of SSI Teaching experience
• Have conducted at least 100 SSI classes at any level
• Have logged at least 400 dives

Option 2:

• Be currently certified as an Advanced Open Water Instructor
• Proof of 3 years teaching experience in the SSI System
• Have certified at least 300 SSI divers at any level.
• Have logged at least 300 dives

Option 3:

• Be currently certified as a Dive Control Specialist Instructor
• Have at least 2 years of SSI Teaching experience
• Have certified at least 200 SSI divers at any level
• Have logged at least 200 dives

Other

Other organizations have different requirements. However, almost all organizations are purely inward looking - certifications or achievements relating to other agencies are disregarded, and in some cases may count against the applicant.

European diver training organizations do not have a direct equivalent. The nearest equivalent within the BSAC system would be National Instructor.

Source

• PADI.com - Master Instructor
• DiveSSI.com - Master Instructor
• BSAC.com - teach diving