This submission explores the development of collaborative computer music creation and the role of the Musical Assistant, or Computer Music Designer, or Live Electronics Designer, or RIM (Réalisateur en informatique musicale) and does so primarily through the consideration of a series of collaborations with composers over the last 18 years. The submission documents and evaluates a number of projects which exemplify my practice within collaborative computer music creation, whether in the form of live electronics, tape-based or fixed media work, as a live electronics performer, or working with composers and others to create original tools and music for artistic creations. A selection of works is presented to exemplify archetypes found within the relational structures of collaborative work. The relatively recent development of this activity as an independent metier is located within its historical context, a context in which my work has played a significant role. The submission evidences the innovative aspects of that work and, more generally, of the role of the Computer Music Designer through consideration of a number of Max patches and program examples especially created for the works under discussion. Finally, the validation of the role of the Computer Music Designer as a new entity within the world of music creation is explored in a range of contexts, demonstrating the ways in which Computer Music Designers not only collaborate in the creation of new work but also generate new resources for computer-based music and new creative paradigms.