The official Rules for Diplomacy
Diplomacy Tournament Guide by Edi Birsan
The Diplomacy Archive's collection of strategy and tactics articles
The Windy City Weasels' guide to improving your play
Strategy Guides from former World Champion Toby Harris:
Strategy articles from the Windy City Weasels.
Diplomacy World (the flagship Diplomacy 'zine) and its strategy archive
The Diplomatic Pouch 'zine
Country-by-country guide from DiplomacyCast (with guest stars):
DiploStrats YouTube channel with commentary and puzzles
Former World Champion Chris Martin's Diplomacy Academy on Youtube
Boston Backbiters FB
Boston Backbiters Discord
New York Diplorats Discord
Windy City Weasels (Chicago)
Bay Area Diplomacy Assoc. (San Jose)
Virtual World Diplomacy Discord