This paper investigates the emergence, development and creative potential of three-dimensional musical scores, examining their transformation from physical layered media to contemporary mixed reality implementations. Through analysis of key historical works and recent technological innovations, it explores how depth and spatial materiality in musical notation create new possibilities for compositional organisation, performance practice and aesthetic expression. The study examines pioneering works utilising transparent overlays and physical depth by composers such as Cage and Takemitsu, before analysing contemporary applications in augmented and virtual reality environments that enable dynamic, interactive score generation and networked performance possibilities. Drawing on phenomenological perspectives and spatial theory, the research demonstrates how three-dimensional scores challenge traditional temporal-spatial relationships in musical notation while suggesting new frameworks for understanding musical structure and interpretation. Technical affordances and limitations of current mixed reality platforms are evaluated, alongside consideration of their implications for future developments in notation and composition. The paper argues that while three-dimensional scores offer compelling new creative possibilities, their successful implementation requires both technological expertise and collaborative approaches that may reshape traditional models of compositional practice.