Letterboxing North America
- Includes a FAQ, links, glossary, and clues for letterboxes all over the United States.
- http://www.letterboxing.org/

Silent Doug's Letterboxing Site
- Articles including getting started, outdoor ethics, a glossary, and an explanation of cryptic letterboxer codes. Also includes a list of boxes found and clues for boxes placed. Most clues are for boxes in the northeastern region of the United States.
- http://www.letterboxing.info

Have Feet Will Travel
- An introduction and guidelines to finding letterboxes on Dartmoor. Includes details of National Park by-laws and contact details for checking military activity.
- http://easyweb.easynet.co.uk/~have.feet/boxing/boxing.html

Dutch Letterbox Site
- Provides information on getting started, codes of conduct, prehistoric Dartmoor and the 100 club.
- http://home.wanadoo.nl/letterboxing/engels.htm

Letterboxing Info Sheet
- An explanation of the hobby for printing out and including in your own letterboxes.
- http://members.aol.com/Letterboxr/infosheet.html

Letterboxing Kids
- Includes a map-reading game, photo album, story and instructions for making rubber stamps.
- http://www.letterboxing.org/kids/