Catastrophic mass flows (CMFs) in the glacial environment are an important geomorphic process that may pose significant hazard to communities and infrastructure in glacierized mountains. CMFs form a broad range of glacial hazards and include mass movements of glacial ice, rock avalanches, iceerock avalanches, glacial debris flows, and outburst-generated flows. Broadly, CMFs in the glacial environment are charac- terized by a sudden onset, high mean velocity (?5 m/s), high mobility (i.e., long runout in relation to volume), and generally involve a mixture of earth materials, water, snow, and ice. In some cases, CMF runout may exceed 100 km from source. CMFs commonly undergo dramatic process transformation during movement in response to melting of entrained ice and snow, entrainment of additional materials along its path, river- damming effects, and incorporation or displacement of water in the periglacial envi- ronment; process complexity thus represents a challenge to quantitative hazard assessment. CMFs initiate in uninhabited glacial environments and frequently descend into denser populated areas where they have an impact on mountain communities and infrastructure. CMFs have been responsible for several notable mountain disasters since 1940, resulting in the death of>15,000 people worldwide. Our focus on an examination of process illuminates an assessment of CMF hazard in glacierized mountain regions and forms the basis for the development of mitigation strategies based on detection, warning, engineering techniques in source and run-out areas, and land-use controls. The precise relationship between the magnitude/frequency of CMFs and cryospheric change in the mountain glacial environment since ca. 1900 remains uncertain.