The ‘Spirit of the Depths’ is one of the governing polarities in Jung’s depth-psychological cosmology, receiving its most sustained formulation in The Red Book: Liber Novus (composed 1913–1930, published 2009). There it stands in dialectical opposition to the ‘Spirit of the Time’ (Zeitgeist): where the latter governs the waking, rationally oriented persona invested in use, value, and collective consensus, the former speaks for the soul, the unconscious, and the timeless substrate of psychic life. Jung personifies this spirit as an autonomous interior authority that compels utterance, resists explanation, and demands that unlived life be lived. The tension between these two spirits is not merely theoretical; in Liber Novus it dramatises Jung’s own confrontation with the unconscious following his break with Freud, and it anticipates his mature typological distinction between Personality No. 1 and Personality No. 2. Secondary commentary within the corpus — particularly the editorial apparatus to Liber Novus — situates this spirit as the structural precursor to Jung’s individuation concept and links it biographically to the decisive reorientation of 1913. The spirit of the depths does not appear as a benign muse alone; it is also the force that drives humanity to self-sacrifice, drags the hero from his solar ascent, and — as one draft passage makes explicit — seized humanity itself through the catastrophe of World War I. Its significance, therefore, spans the intrapsychic and the historical.