Dam Failure Mechanisms and Risk Assessment introduces the causes, processes and consequences of dam failures as well as risk assessment and decision methodologies for dam failure emergency management. It begins with a physical understanding of two most common failure mechanisms: internal erosion and overtopping erosion. Such understanding is substantiated by presenting the updated statistics of failures of large dams and landslide dams based on the most recent dam-failure databases compiled by the authors. The last version of statistics of dam failures was presented by the International Commission on Large Dams in 1995. Subsequently, methods for determining dam breaching parameters such as breach geometry and peak flow rate and analyzing the dam breaching flood routing in the downstream river are presented. Afterwards, how the human, property and environment elements in the flooded zones are vulnerable to the dam-breaching floods are assessed and the associated risks assessed quantitatively. Finally methodologies for optimal decision making under uncertainty for risk mitigation are described.