Psychic fluidity designates the capacity of psychic contents, images, and energy to move, transform, dissolve, and recombine rather than remaining fixed in rigid configurations. Within the depth-psychology corpus the term occupies a contested space: it is simultaneously a desideratum of psychological health, a description of the unconscious’s native mode of operation, and a potential hazard when fluidity shades into dissolution without structure. Jung’s energic model frames fluidity as intrinsic to the psyche’s quantitative-qualitative nature — the psyche must be understood as ‘mass in motion,’ its intensities in perpetual gradient shift. The alchemical tradition, as read by Jung, Edinger, and Hillman, supplies the richest imagery: nigredo, putrefaction, and mortification break down fixation so that the opus may advance through liquefaction and eventual coagulation into new form. Giegerich’s index entry ‘liquefaction, liquidity (→ fluidity)’ signals that in post-Jungian dialectical psychology, fluidity is the soul’s own logical movement, not merely a therapeutic metaphor. Von Franz situates fluidity at the infrared pole of the psychic spectrum, where psyche flows into matter. Tarnas maps a Neptunian archetype of boundary-dissolution that encompasses both mystical union and pathological diffusion. The tension between generative fluidity and ego-threatening dissolution remains the field’s central diagnostic problem.