This review compiles and contextualizes the available empirical literature on natural occurrences of high-stakes altruism among nonrelatives, i.e., behaviors often called ‘heroic’. Four domains are covered: exceptional bravery and self-sacrifice in war, heroism in civilian life, undirected organ donations, and rescues of persecuted persons during mass violence and genocides. The diversity of strategies used to identify instances of heroic behavior and the multiplicity of data collection methods employed in this relatively sparse literature currently preclude a systematic comparison of results. Therefore, the aim of this overview is to provide an exhaustive point of entry to a fascinating field of research with much untapped potential for testing theories about prosocial behavior.