This chapter discusses aspects and causes of extreme events and lays out an overview pertinent to the notion of extreme events regarding definitions and drivers. Three angles for defining an extreme event are taken: a literary, mathematical, and regulatory angle. There is currently a plethora of definitions; there is a need for a unified definition of extreme events. There is a string of causes of extreme events, and most of these drivers are due to human behavior, such as lack of imagination, complacency, poor understanding of network linkages, reckless behavior, or strategic mistakes. Finally, research shows that the environment for banks and for corporates shows similarities that can be traced back to the aspects of complexity and uncertainty. Extreme events are not always outliers because the environment in which banks and disruption-prone companies operate is extreme due to the growing complexity and uncertainty.