US-based portal offering FAQ, links, forums, and a members-only section where clues can be submitted.

Community with forums, searchable clues, trip planner, recording of finds, event listings, trackers, tutorials, photo galleries, and chat room.

Database of clues to letterboxes in urban locations, primarily in Europe.

Articles including getting started, outdoor ethics, and explanation of cryptic letterboxer codes. Also includes list of boxes found and clues for boxes placed in the northeastern region of the United States.

Includes a forum, image gallery, map of the area, contact details, and the history of the activity.

Discussion group for US letterboxers.

Clues for Germany and other European countries. Includes photos and tips. [English, German]

Discussion forum and articles for those new to letterboxing.

Introduction, tips and things to avoid, news, survey, and letterbox clues for the Dartmoor area.

Weblog about his letterboxing hobby.