This thesis examines the nature of individual differences in approach to design practice, concerning a practitioner's relationship with the medium with which they work, and its role in their practice. It does so with a view to developing future digital environments for creative practice. Most existing computer systems for 3D design and modelling have developed around the 'design-by-drawing' paradigm. Recent advances in digital technologies offer more direct manipulation of models in 3D space through touch, bringing the more immediate ways of working with materials associated with other approaches to design within the realm of digital systems. A previous investigation of an alternative paradigm for future computer systems, the working processes of designer-makers, was undertaken to better understand the role of materials within their processes. This revealed differences in individual approach: some practitioners developed their ideas using sketching, while others chose to work with materials (either to design, or making with the medium), or combined both. Reporting on initial enquiries concerning such practitioners' preferences for working in two or three dimensions to generate design ideas, this thesis suggests that there are more fundamental differences between individuals in their relationship with the medium in which they work. However there exists little design literature to assist in this regard. Drawing on literature on creative processes from other disciplines, including writing and computer programming, it proposes that differences exist between individual design practitioners which are more significant than variation arising from each designer's personal style, unique experience, or working context; rather they represent wholly different approaches to design, elements of which relate to the nature and extent of a dialogue between practitioner and medium. A systematic analysis of this literature suggested the formal/concrete axis is an organising principle for differences in approach across disciplines and across a number of levels of practice. An investigation was undertaken to determine whether similar differences in approach could be observed between 3D design practitioners. Using primarily interview methods, but also set tasks and observation, three empirical studies were conducted to examine in detail the creative practices of students and professional practitioners working with three- dimensional media, both material (silversmithing and jewellery, textiles, sculpture) and digital (3D computer graphics and animation, 3D modelling, 3D immersive digital environments). The results demonstrate that important underlying differences exist between individual design practitioners, concerning their relationship with the medium with which they work, and its role in their practice. This thesis concludes that while elements of these differences in approach can indeed be mapped directly to a formal/concrete axis, others cannot, and proposes avenues for further exploration. This examination of differences in approach demonstrates an underlying commonality between disciplines including 3D design practice, writing and computer programming as regards how practitioners work, and their relationships with the medium they work in, on or through. It indicates important aspects of working and knowing that are not embedded in the material context of practice, which should be acknowledged by theory, and could be harnessed practically in the development of future digital environments for creative practice.