Gygax developed the core medieval system of the game by expanding on rules authored by his fellow Lake Geneva Tactical Studies Association (LGTSA) member Jeff Perren, a hobby-shop owner with whom he had become friendly.

[3] Gygax edited and expanded these rules, which were published as "Geneva Medieval Miniatures", in Panzerfaust magazine (April 1970), using 1:20 figure scale.

[4][6] The fantasy supplement also referenced the works of J. R. R. Tolkien, Robert E. Howard, Poul Anderson, and Michael Moorcock.

[2] Both Perrin and Gygax "swiped" Coggin's artwork to illustrate their preliminary articles about Chainmail that appeared in Panzerfaust and The Domesday Book.

A set of mass-combat rules, heavily indebted to the medieval systems of Tony Bath and intended for a 1:20 figure scale.

Additional rules govern missile and artillery fire, movement and terrain, charging, fatigue, morale, and the taking of prisoners.

[12] A set of man-to-man combat rules (for 1:1 figure scale), ultimately deriving from a contribution to Domesday Book #7.

The core of these rules became the Appendix B chart mapping various weapon types to armor levels, and providing the needed to-hit rolls for a melee round.

These rules were originally designed for postal play; members of the C&CS could participate in jousting tourneys in order to raise their standing in the Society.

The first edition Chainmail fantasy supplement added such concepts as elementals, magic swords, and several spells including "Fireball" and "Lightning Bolt".

[citation needed] Creatures were divided between Law and Chaos, drawing on the alignment philosophies of Poul Anderson, as popularized by Michael Moorcock's Elric series.