The risk management of natural hazards is a complex issue often due to very significant potential consequences and substantial uncertainties. A framework for risk based decision making in the field of engineering is first described in this paper. This framework is then applied for the risk assessment of volcanic hazards. Towards this end, aspects related to the modeling of the hazard process due to volcanoes are described. A system of classification of structures and identification of different building characteristics that could be used for volcanic vulnerability and risk assessment is then proposed. This is followed by a discussion on the fragility and vulnerability modeling of structures. Finally, general issues concerning the evaluation of risks and their treatment and communication are discussed.