This is mainly a summary and criticism of the papers read at the symposium on 'The Concept of Aggression' held by the British Psychological Society in 1938. The author is chiefly concerned to effect a clarification of the terms employed. He also makes the interesting point that since the important self-preservative reaction of aggression requires practice and expression in real life, it is essential for the individual to experience actual danger and fear; and he cites the case, observed by himself, of an over-protected child who used to amuse himself by playing at being afraid.