This special issue is devoted to the cancerchemopreventive effects of the trace element selenium. Although epidemiological and animal model studies have contributed enormously to this field, the clinical trial headed by the late Dr. Larry Clark brought to light the very real possibility that selenium compounds may serve as protective agents in populations at risk for prostate, colon, and lung cancers. For this reason, experts from various disciplines have been brought together to address the current state of the knowledge of the role of selenium as an anticancer agent. It is hoped that by bringing these various approaches together in one place, the research community, both graduate students and established investigators, can better grasp the complex nature of this field. The papers in this issue cover the entire spectrum of cancer research, ranging from clinical trials to animal model studies and molecular biology.