During October 18-30, 1981, the second course of the International School of Pure and Applied Biostructure, a NATO Advanced Study Institute, was held at the Ettore Majorana Center for Scientific Culture in Erice, Italy, co-sponsored by the International Union Against Cancer, the Italian League Against Cancer, the Italian Ministry of Public Education, the Italian Ministry of Scientific and Technological Research, the North Atlantic Treaty Organization, the Italian National Research Council, the Sicilian Regional Government and two pharmaceutical Companies (Zambeletti and Farmitalia). The subject of the course was "Chemical Carcino­ genesis" with participants selected world-wide from 18 different countries. It is now eminently clear that.the bulk of human cancers are related to one of several types of environmental exposure. Of the environmental hazards, chemicals are among the best characterized carcinogens. However, how chemicals induce cancer is still poorly understood. Because of the magnitude of the problem and the ob­ vious need for a much more critical scientific analysis of the process by which cancer is induced (carcinogenesis), it was highly desirable to expose a greater number of scientists with varying background to some of the latest thinking in chemical carcino­ genesis. The course had this as its major objective and the re­ sulting book does reflect it.