An introduction to risks and hazard in the environment. Different types of hazards are analyzed and compared: natural disasters, such as tornados, earthquakes and meteorite impacts; acute and chronic health effects caused by exposure to radiation and toxic substances such as radon, asbestos and dioxin; long-term societal effects due to environmental change, such as sea level rise and global warming. Emphasizes the basic physical principles controlling the hazardous phenomena and develops simple quantitative methods for making scientifically reasoned assessments of the threats (to health and wealth) posed by various events, processes and exposures. Discusses methods of risk mitigation and sociological, psychological and economic aspects of risk control and management.