Puer Aeternus is Latin for Eternal Boy. In Jungian Analytical Psychology, examples of the puer archetype include the child, young boy or adolescent. The term can also be applicable to females in which case the Latin terminology is Puella.

Puer Aeternus: A Psychological Study of the Adult Struggle With the Paradise of Childhood and The Problem of the Puer Aeternus are books that Jungian analyst Marie-Louise von Franz wrote about a specific instance of the archetype, the puer aeternus (or "eternal youth"), which includes such figures as Peter Pan and The Little Prince in the book of the same name by Antoine de Saint-Exupéry. Mozart as portrayed in the movie Amadeus demonstrates the puer archetype.

Analytical psychologists claim that the puer archetype can lead to psychological problems which are manifest by immaturity, narcissism and an inabilty to develop a properly adult perspective on life.

The antithetical archetype, or enantiodromic opposite, of the puer is the senex.

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