Prima materia occupies a foundational position in the depth-psychological reading of alchemy, functioning simultaneously as cosmological substrate, psychological metaphor, and therapeutic concept. Jung establishes the term’s central paradox: it is ‘cheap as dirt and can be had everywhere, only nobody knows it,’ possessing a ‘thousand names’ that mark its essential elusiveness — chaos, hyle, massa confusa, Saturn, Adam, the sea, quicksilver. For Jung, the prima materia projects the contents of the unconscious into matter; the alchemist’s search for first substance is therefore a search within. Edward Edinger extends this insight clinically, reading the prima materia as the undifferentiated psychological state — pure potentiality from which new form emerges — and identifying it with the infant, the child, the dreamer returned to origins. Abraham’s lexicographic work establishes the iconographic range: Adam, Mercurius, the hermaphrodite, the sea, argent vive, and earth all serve as synonyms within the alchemical tradition. Von Franz situates the prima materia within the micro-macrocosmic framework, where the opus on first matter mirrors God’s creation of the universe. The Platonic substrate, most visible in the Timaeus, supplies the philosophical grammar: a formless receptacle that must be without character in order to receive all forms. Tensions persist between those who emphasize the prima materia’s universal accessibility and those who stress the arduous labour required to produce or identify it.