The major objective of the study was to develop a series of principles and recommendations that may serve as the basis for assessing the genotoxic hazards of environmental agents. It was considered that such principles and recommendations would be useful in setting priorities for the regulation and control of the vast array of chemicals to which humans are exposed in the environment; in formulating guidelines or regulations to mitigate the genetic effects of environmental agents; and in designing appropriate mechanisms to minimize the effects of such agents on both humans and other living organisms. This book is based on the working papers that resulted from the study.