Americana Unit: History, culture, and industry of the USA worldwide.
American Society of Polar Philatelists: Antarctica and Arctic.
Archaeological Study Unit: The Archaeology Study Unit collects and studies postage stamps related to archaeology from the stone age to the beginnings of recorded history..
Armenica (Armenian Philatelic Association): Armenian history and culture worldwide.
Astronomy Study Unit: Astronomy, astrophysics, comets, planets.
Bicycle Stamps Club: Bicycles.
Biology Unit: Worldwide animal and plant life, present and prehistoric.
Captain Cook Society: Life and voyages of Captain James Cook.
CartoPhilatelic Society: Globes and maps.
Casey Jones Railroad Unit: Trains, railroads, and streetcars.
Cats on Stamps Study Unit: Domestic and wild felines.
Chemistry & Physics Study Unit: Chemistry, physics, and related science.
Chess on Stamps Study Unit: Chess and other board games.
Christmas Philatelic Club: Sacred and secular aspects of Christmas.
Disneyana on Stamps Society: Philatelic items relating to Walt Disney and his legacy.
Ebony Society of Philatelic Events and Reflections (ESPER): African American heritage worldwide.
Errors, Freaks & Oddities Collectors Club: Errors, freaks, and oddities on worldwide stamps.
Europa Study Unit: All aspects of a United Europe.
Fire Service in Philately: Firefighting.
Gastronomy Study Unit: Food, ingredients, cooking, and food science.
Gay & Lesbian History on Stamps Club: LGBQT history and culture.
Gems-Minerals-Jewelry Study Unit: Gems, jewelry, and minerals.
Graphics Philately Association: Books and printing from papyrus to eBooks.
International Society of Worldwide Stamp Collectors: Worldwide stamp collecting.
Journalists, Authors and Poets on Stamps (JAPOS): Authors, journalists, and poets.
Lighthouse Stamp Society: Lighthouses worldwide.
Malaria Philatelists International: Malaria worldwide.
Masonic Study Unit: Freemasonry.
Medical Subjects Unit: Dentistry, nursing, pharmacy, physicians, Red Cross and veterinary medicine. Email contact Mike Clark (mclark577[at]gmail.com).
Motivgruppe Musik: Music worldwide.
N. S. Savannah Study Unit: Nuclear ship N. S. Savannah (USCS Chapter 109).
Penguins on Stamps Study Unit: Penguins.
Perfins Club: Stamps with perforated initials, numbers, or designs.
Petroleum Philatelic Society International: Oil, natural gas, and petrochemical industry.
Pitcairn Islands Study Group: Pitcairn settlers past and present.
Plate Number Coil Collectors Club (PNC3): Plate numbered coils and related stamps.
Rotary on Stamps Fellowship: Rotary International.
Scouts on Stamps Society International: Scouting worldwide.
Ships on Stamps Unit: All types of watercraft.
Space Unit: Astronauts and astronautics.
Sports Philatelists International: Olympics, recreation, and sports.
Stamps-on-Stamps Collectors Club: Stamps-on-stamps.
United Nations Philatelists: United Nations worldwide.
Windmill Study Unit: Molinology.
Wine on Stamps Study Unit: Grapes, wine, and winemaking.