Digital music technologies, and instruments in particular, are the result of specific systems of thought that define and enframe the user’s creative options. Distinctive divisions between digital and acoustic instruments can be traced, contrasting the conceptually based design of software with the affordances and constraints of physical artefacts. Having lost the world’s gift of physical properties, the digital instrument builder becomes more than a mere luthier. The process of designing and building the instrument is transformed into a process of composition, for it typically contains a greater degree of classification and music theory than its acoustic counterpart. Part I of this thesis begins by framing musical systems in the context of the philosophy of technology. Here technological conditions are questioned and theories introduced that will assist the investigation into the relationship between creativity and technology. After this general grounding, the ramifications digital technologies pose to the human body are explored in the context of human expression through tool use. The human-machine relationship is described from phenomenological perspectives and relevant theories of cognitive science. This analysis serves as a foundation for the concept of epistemic tools, defined as the mechanism whereby techno-cultural models are inscribed into technological artefacts. The cultural element of tool use and tool origins is therefore emphasised, an aspect that is highly relevant in musical technologies. Part I thus frames the material properties of acoustic and digital instruments in relation to human culture, cognition, performance and epistemology. Part II contextualises these theories in practice. The ixiQuarks, the live improvisation musical environment that resulted from the current research, are presented as a system addressing some of the vital problems of musical performance with digital systems (such as the question of embodiment and theoretical inscriptions), proposing an innovative interaction model for screen-based musical instruments. The concept of virtual embodiment is introduced and framed in the context of the ixi interaction model. Two extensive user studies are described that support the report on ixiQuarks. Furthermore, comparative surveys on the relationship between expression and technology are presented: a) the phenomenology of musical instruments, where the divergence between the acoustic and the digital is investigated; b) the question of expressive freedom versus time constraints in musical environments is explored with practitioners in the field; and c) the key players in the design of audio programming environments explain the rationale and philosophy behind their work. These are the first major surveys of this type conducted to date, and the results interweave smoothly with the observations and findings in the chapters on the nature and the design of digital instruments that make up the majority of Part II. This interdisciplinary research investigates the nature of making creative tools in the digital realm, through an active, philosophically framed and ethnographically inspired study, of both practical and theoretical engagement. It questions the nature of digital musical instruments, particularly in comparison with acoustic instruments. Through a survey of material epistemologies, the dichotomy between the acoustic and the digital is employed to illustrate the epistemic nature of digital artefacts, necessitating a theory of epistemic tools. Consequently virtual embodiment is presented as a definition of the specific interaction mode constituting human relations with digital technologies. It is demonstrated that such interactions are indeed embodied, contrasting common claims that interaction with software is a disembodied activity. The role of cultural context in such design is emphasised, through an analysis of how system design is always an intricate process of analyses, categorisations, normalisations, abstractions, and constructions; where the design paths taken are often defined by highly personal, culturally conditioned and often arbitrary reasons. The dissertation therefore dissects the digital musical instrument from the perspectives of ontology, phenomenology and epistemology. Respective sections in Part I and Part II deal with these views. The practical outcome of this research – the ixiQuarks – embodies many of the theoretical points made on these pages. The software itself, together with the theoretical elucidation of its context, should therefore be viewed as equal contributions to the field of music technology. The thesis closes by considering what has been achieved through these investigations of the technological context, software development, user studies, surveys, and the phenomenological and epistemological enquiries into the realities of digital musical instruments, emphasising that technology can never be neutral.