Recent developments are presented in the evolution of Harmony Space, a highly enabling interface designed to encourage and facilitate rapid learning, especially by beginners, about the practical use and theory of tonal harmony, especially as applied to composition and analysis. The interface exploits both cognitive theories of tonal harmony and principles of human-computer interaction. In particular, the design of the interface draws on Balzano's and Longuet-Higgins' theories of tonal harmony. The interface allows entities of interest (notes, chords, chord progressions, key areas, modulations) to be manipulated via direct manipulation techniques using a single principled spatial metaphor. This makes it possible for novices to learn to perform a wide range of musical tasks involving harmony relatively quickly. The interface can also be used by experienced musicians to gain new insights and perform certain tasks much more easily than with conventional tools and notations. The interface is highly interactive and multi-modal, using two pointing devices and spatial, aural and kinaesthetic cues that all map uniformly into the underlying representation. Some recent implementations of Harmony Space are discussed, together with some of the musical tasks which they make tractable for beginners and experienced musicians. Aspects of the simple, consistent, principled framework behind the interface are outlined
