If we can add words: There are at least a handful of philatelic libraries in the United States, and more around the world. Our list focuses on U.S. sources with significant digital resources for your ready use.
American Philatelic Society
The national stamp collecting organization. Garfield-Perry is the 3rd Life Chapter
APS Certificate Archive
Searchable Index of APS Expertizing Service Certificates
National Postal Museum
This site is the doorway into our National Postal Museum, part of the Smithsonian. Be sure to look at the “Learn & Explore” section of this site
U. S. Postal Bulletins
Digitized U.S. postal bulletins, as well as postal laws and regulations
U.S. Post Offices
A list by state, county and office with dates the offices opened (and closed)
Finding U.S. Postmasters
A list on the U.S. Postal Service site of most U.S. postmasters
Colnect
An online listing of World-Wide stamps with variations.
Stamp Finder
A place to help identify the origin of stamps, mostly from the words on the stamps
Doane Cancels
A site with descriptions of Doane canceling devices and the places where they were used
North Carolina Postmarks
A regularly updated online catalog of North Carolina postmarks
Free Classic and Modern Philatelic Literature
Translated Philatelic Words and Phrases
Common philatelic words translated between English, French, German, Italian, Portuguese and Spanish
The Saks Stamp Overprint Encyclopedia
Listing overprints from A to Z
Saks World Overprint & Stamp ID
A listing of words found printed on stamps and their descriptions