You will need THE BOOK OF JADE itself, and a copy of the core rule-set of IRONCLAW.
If you want the bare minimum to play, you will need to pledge either "A GARDEN CARRIED IN THE POCKET" (for digital versions) or "A SHUT BOOK IS BUT A BLOCK OF PAPER" (for printed versions).
IRONCLAW's basic rules are available in two different volumes:
* THE PLAYER'S BOOK, which includes the rules for making basic characters and for how the characters interact.
* THE OMNIBUS, which includes all the material from the Player's Book and advanced material on how to play in the land of Calabria, including its greater mysteries, powerful magics, and strange wilding ways.
The Players' Book and the Book of Jade together is all you would need to play the game. While the Omnibus includes all the Players' book information, the details of Calabria aren't necessary if you're adventuring in the Middle Kingdom of Zhongguo.