Definitions of ‘stress’ are presented and discussed, and a distinction is made between biological and psychological concepts of stress. All relevant concepts from the 1930s to the present day are discussed. Similarly, the term post-traumatic stress disorder (PTSD) is defined and placed in its historical research context. A foundation for the subsequent investigations is also laid on the subject of impact research in psychology. Finally, the focus is on the topic of critical incident stress management (CISM), whose historical development and practical applications are presented and discussed.