The APS is the largest, nonprofit society in the world for stamp collectors. It is supported entirely by membership dues, gifts, and the sale of its publications and services. Founded in 1886, the APS is now in its second century of service to stamp collectors and postal historians.

The AFDCS is a volunteer non-profit and non-commercial organization serving the needs of First Day Cover collectors, cachet makers, and dealers. Founded in 1955, the society now has a membership of nearly 3,000 active first day cover collectors, including hundreds of collectors who design and manufacture their own cacheted FDCs.

The American Topical Association serves members in 90 countries. It is the largest philatelic society devoted to a specific phase of stamp collecting. Organized in 1949, the ATA has over 50 years of service to its members. The ATA is the best source of information, fellowship and inspiration in the topical field.

Young Stamp Collectors of America is a club for collectors under 18. Whether you are new to the hobby or have collected for several years, the YSCA offers a variety of ways to make your collecting more fun.

The YPLF is a A program that engages young stamp collectors in the most exciting elements of the philatelic world.  Along with mentoring from seasoned collectors, dealers, exhibitors and authors from varied backgrounds and expertise, Fellowship members will have opportunities to travel and develop a year-long project in one of several philatelic areas.

The Post Mark Collectors Club (PMCC) is an International Organization committed to the preservation of postal history and encouraging the hobby of Post Mark collecting. The club is a non-profit affiliate of the American Philatelic Society. 

The United Postal Stationery Society is a non-profit organization which was formed in 1945 through merger of the Postal Card Society of America and the International Postal Stationery Society.  It is the largest society devoted to the collecting of postal stationery with members across the United States and countries throughout the world.

The U.S. Philatelic Classics Society is the successor of "The Three Cent 1851-57 Unit" (Unit Number 11) of the American Philatelic Society. It was originally founded by a group of '51 to '57 specialists that included Dr. Carroll Chase, Stanley B. Ashbrook, and Leo J. Shaughnessy. Since its founding, the Society has broadened its scope to include postal issues and postal history from the Stampless era up to the Bureau Issues.

The USCS, an international philatelic organization founded in 1932 has over 1,500 members with an interest in postmarks and covers from all maritime services. This includes Navy ships of all countries, Marine Corps, Coast Guard, Navy bases, merchant ships with seapost and paquebot markings, related cachets, and other naval memorabilia. It is the only organization in the U.S. devoted to Navy and maritime covers.