From publisher blurb: Old School Fantasy Roleplaying: Skills provides alternate rules for adjudicating and using skills for the classic versions of the most famous fantasy roleplaying game in the world commonly referred to under various abbreviations: Zero Edition, Holmes Basic, Basic/Expert, B/X, Mentzer Basic, BECMI, RC, 1st Edition, and 2nd Edition. Basically, these rules work best with any version before the 3rd Edition of the game.