Rules of Play is a book on game design to be published later this year (with a chapter from Reiner Knizia):

Games have become as much a genre of pop culture as film or television, but game design has yet to develop a theoretical framework or critical vocabulary. In Rules of Play Katie Salen and Eric Zimmerman offer an impassioned defense and definition of this emerging field. Their goal is to create a unified methodology for looking at all kinds of games and to understand game design as a design practice. The authors, active participants in game culture themselves, intend their book to act as a catalyst--to help game designers explore new ways to create games and develop concepts, design strategies, and methodologies.

(via Terminal City Gamers)