<p>This thesis documents three years of extensive research into the field of sonic spatial expression and is the culmination of years of fascination about all of the ways music is made. In particular, it focuses on the way sounds move through space. This research stems from artistic practice and a desire to deeply explore spatial aesthetics in sound art. A potential for further development of tools designed for aesthetic engagement with spatial attributes of music is identified. It is proposed that with new tools designed for the manipulation of spatial attributes, new spatial aesthetics might emerge. In exploring this proposition, a number of contributions to the field of spatial sound art are presented. The main approach taken is to apply new technologies to the design of spatialisation performance interfaces. It is hoped that in designing novel interfaces that specifically engage with spatial parameters, new ways for aesthetically engaging with space will be afforded for composers and performers. The tools designed all aim to exhibit a high level of intuitiveness in their control systems, allowing non- expert users access to these spatially expressive tools. Additionally, the new tools aim to provide high levels of expressivity so that advanced composers who are looking for new ways to use space expressively may also use them. This thesis focuses on the design, development, implementation, analysis, and artistic use of new spatial interfaces. The design methodology implemented for all of the interfaces includes both testing and analysis phases that involve the composition and performance of new musical works. The development of the interfaces is closely coupled with the development of the new musical works, with each design phase applied to a new work and each new work or spatial idea exploring the new aesthetics afforded by the tools. The assessment of these new tools takes various forms: they are assessed by critical evaluation of the new works created, by user study evaluations from other composers who utilise the tools, and, where appropriate, by quantifiable methods of evaluation that are adopted to assess specific spatialisation tools. The new musical interfaces presented, described, and evaluated in this document were conceived of as musical instruments, each affording new approaches to spatial expression. This document also details an extensive collection of new musical works that feature the interfaces. It concludes by suggesting future directions for this research body and the spatialisation interface design field.</p>