Many factors can lead to volcano lateral collapse, which can produce devastating debris avalanches that travel up to several tens to over 100 km and cover hundreds to more than a thousand km2 with debris. Volcanic lateral collapses are severe hazards because of their destructive power and size, and sudden onset. Although their frequency of occurrence is not as high as those of smaller volcanic mass movements, such as rock falls and lahars, globally large collapses ≥0.1 km3 have occurred at least five times per century over the last 500 years. A large variety of destabilizing factors such as over-steepened slopes, magma intrusions, hydrothermal activity, climate fluctuations, deformation of the basement, and faulting can create the conditions for volcano collapse. Once a volcano reaches its critical point, a mechanism is necessary to trigger the failure event. We present the state-of-the-art of the knowledge acquired in the last few decades concerning the causes of large-scale volcanic failures to better understand the triggers, preparatory factors, and timing of volcano lateral collapse.