These products provide information and mechanics for both games systems: the second edition of the Legend of the Five Rings rpg and the Oriental Adventures sourcebook for Dungeons and Dragons. In the latter case they build on the material presented in the Rokugan sourcebook.
The common text presented on the back of all these products is:
This book is a dual-system supplement for the Legend of the Five Rings Role-Playing Game, Second Edition, and Rokugan, the d20 Companion for Legend of the Five Rings. Players and DMs may also find it useful as a source of interesting new feats and abilities for any d20 System campaign.
Game Masters running the Second Edition L5R RPG will need a copy of the Legend of the Five Rings Game Master's Guide and the Player's Guide. Players need only the Player's Guide.
Dungeon Masters running d20 System games will need a copy of the Player's Handbook, the Dungeon Master's Guide, Oriental Adventures, and Rokugan. Players will need only a Player's Handbook.