The Fountain of Youth occupies a surprisingly rich stratum in the depth-psychology corpus, operating simultaneously as a mythic motif, an alchemical symbol, a psychodynamic metaphor, and a neuroscientific provocation. Jung locates its psychological core in the dynamics of the libido: when psychic energy turns inward and descends to the unconscious depths — the ‘underworld’ — it may return as renewed vitality, making the journey to the underworld structurally equivalent to a plunge into the fountain of youth. This reading transforms the archaic myth into a paradigm of individuation and psychic renewal. The alchemical tradition supplements this with the mercurial fountain (fons mercurialis), the aqua permanens that dissolves, purifies, and resurrects base matter — a chemical allegory for psychological transformation. Campbell maps the theme across world mythology, finding it in Gilgamesh’s dive to the cosmic sea’s floor for the plant of immortality, in Taoist longevity lore, and in the logic of the hero’s return from the underworld. Onians and Rohde anchor the motif in archaic European and Near Eastern beliefs about life-liquid, sacred waters, and the restorative power of divine dew. Panksepp, strikingly, reframes the search in neurobiological terms, arguing that the PLAY system and its brain chemistries constitute a modern scientific equivalent of the Fountain of Youth quest. Across these positions, the term consistently marks the threshold between mortal finitude and renewed or immortal life.