As of 2026-10-12, Institute of Electrical and Electronics Engineers tops the list with 423,000 members.
- #1 Institute of Electrical and Electronics Engineers — 423,000 members
American professional association for electronic engineering and electrical engineering
The Institute of Electrical and Electronics Engineers is an American 501(c)(3) charitable professional organization for electrical engineering, electronics engineering, and related disciplines. Read more on Wikipedia.
Wikidata - #2 AAPC — 300,000 members
American Academy of Professional Coders
The AAPC, previously known by the full title of the American Academy of Professional Coders, is a professional association for people working in specific areas of administration within healthcare businesses in the United States. AAPC is one of a number of providers who offer services such as certification and training to medical coders, medical billers, auditors, compliance managers, and practice managers in the United States. As of September 2025, AAPC has over 300,000 worldwide members. Read more on Wikipedia.
Wikidata - #3 German Teachers' Association — 165,000 members
voluntary association
source Wikidata - #4 Marburger Bund — 150,625 members
largest medical association in Europe
source Wikidata - #5 American Psychological Association — 146,000 members
scientific and professional organization headquartered in the Washington, D.C.
The American Psychological Association (APA) is a professional organization of psychologists in the United States, and the largest psychological association in the world. It has over 190,000 members, including scientists, educators, clinicians, consultants, and students. It has 54 divisions, which function as interest groups for different subspecialties of psychology or topical areas. Read more on Wikipedia.
Wikidata - #6 Society of Petroleum Engineers — 124,833 members
not-for-profit professional organization
The Society of Petroleum Engineers (SPE) is a 501(c)(3) not-for-profit professional organization. Read more on Wikipedia.
Wikidata - #7 American Welding Society — 73,000 members
organization
The American Welding Society (AWS) was founded in 1919 as a non-profit organization to advance the science, technology and application of welding and allied joining and cutting processes, including brazing, soldering and thermal spraying. Read more on Wikipedia.
Wikidata - #8 Bayerischer Lehrer- und Lehrerinnenverband — 61,000 members source Wikidata
- #9 Bundestierärztekammer — 43,000 members
eingetragener Verein
source Wikidata - #10 California Society of Certified Public Accountants — 42,000 members
Professional association of certified public accountants in California
The California Society of Certified Public Accountants (CalCPA) is the largest statewide professional association of certified public accountants in the United States with more than 42,000 members. Read more on Wikipedia.
Wikidata