This second edition is fully updated throughout and covers the emerging evidence that indicates that the Gadd45 family of proteins plays a unique and critical role as sensors of stress, including genotoxic, physiological, and oncogenic stress. It sheds light on the complex cellular stress response, encompassing myriad molecular pathways with a plethora of regulators and effectors. The GADD45 stress response genes encode small (18 kd) nuclear/cytoplasmic proteins. These genes are rapidly induced by a wide variety of endogenous and exogenous stress stimuli. Despite marked similarities, Gadd45 genes are regulated differentially and exhibit functional diversity. Gadd45 proteins respond to physiological and oncogenic stress, and are implicated in