This book on major risks provides some general elements, a description of prevention and protection measures, general instructions to follow, casualty compensation and of global risk management. The recent events showed that France, like other nations, could be affected by major disasters. since risk zero does not exist, the strengthening of a culture of safety makes it possible to reduce vulnerability. Thus, this general guide proposes to explain the risk mechanisms and to provide brief replies to the most frequent interrogations. It reviews the various types of natural risks(floods, volcanoes, earthquakes, landslides, avalanches, forest fires, cyclones and storms) and technological risks (nuclear, industrial, dangerous materials transportation and dam breaks. (UNEsCO)