Engineering Design Re-use refers to the utilisation of any knowledge gained from the design activity to support future design. As such, Engineering Design Re-use approaches are concerned with the support, exploration and enhancement of design knowledge prior, during and after a design activity. Modular Design is a product structuring principle whereby products are developed with distinct modules for rapid product development, efficient upgrades, and possible re-use (of the physical modules). The benefits of Modular Design centre of a greater capacity for structuring component parts to better manage the relation between market requirements and the designed product. This work explores the capabilities of Modular Design principles to provide improved support for the Engineering Design Reuse concept. The Modular Design principle is extended to structure not only the artefact's components but also their associated knowledge, to support, explore and enhance the knowledge genera ted during the evolution of the design process. A novel modular design approach, termed a Multi-Viewpoint Modular Design Methodology, is developed to address identified requirements including; support for evolutionary design knowledge, exploration and identification of inherent modularity and maintenance of the modular solution. The overall concept of the Methodology is to support the designer in evolving a modular artefact whilst utilising the principles of modularity to structure the artefact knowledge to enhance its potential applicability for re-use, the concept is termed knowledge modularity. Based on the results of a state of the art review deficiencies of existing approaches are identified including; insufficient support of evolutionary design knowledge, insufficiencies in the modelling, exploration, identification and representation of knowledge modularity, limitations in the module identification process. Declarative and procedural knowledge is developed to define a novel Modular Design Methodology to address these deficiencies. As such, the Methodology presents a formalised approach to support the modelling, optimisation and identification of modularity, both within and across viewpoints (function, working principle and structure) of the product structure, and evolutionary design knowledge. The core phenomena of a knowledge module is formalised in terms of the knowledge of design concepts and their dependencies. The formalism supports the identification of inherent modularity. An alternative model, termed the Modular Structure Matrix is developed as part of the Methodology to represent this inherent modularity. In addition, the Methodology has been developed, through a 12-month industrial residency, to address the requirements of practising designers. The Methodology is applied throughout a design activity to formalise and represent (in a matrix formalism) knowledge of the concepts embodied by a design artefact. The resulting model provides the basis to determine and represent interdependency knowledge between design concepts. The modelled concept and dependency knowledge can be utilised to support a modular analysis of the product structure both within and across design viewpoints. An optimisation and module identification mechanism can then be applied to the model and, based on the dependency data, identify inherent modularity within individual viewpoints of the product structure. Further, a mapping methodology has been developed to support the maintenance of the modular solution, and its associated artefact knowledge, across multiple viewpoints of design. The new methodology can be applied in a cyclic and iterative manner to support modularisation of the artefact design knowledge through the evolution of the design. A computational implementation has been developed to aid the evaluation of the Methodology. The functionality ofthe Methodology has been illustrated through two literature based case studies and two industrial implementation evaluations. An implementation and evaluation methodology was formalised through the rationalisation of the activities carried out during the first, and further utilised as the basis to support the second, industrial implementation. The two literature based studies evaluate the functionality of the methodologies optimisation and module identification mechanisms. These evaluations result in the identification of modular hierarchies that were not evident in the findings of the original publications. In addition, both industrial implementations result in the identification of potential improvements in the design. The evaluations illustrate the functionality of the Methodology in identifying and maintaining modularity, structuring design knowledge, supporting decision-making, learning, and improving design understanding. In addition, the evaluators outlined further potential Methodology application fields such as team design, manufacturing design and technology life-cycle management. Further the strengths and weaknesses of the Methodology, the computational implementation, and the research methodology utilised to facilitate the work presented in this thesis, are discussed. Finally, future work required to enhance the capabilities of the Multi- Viewpoint MD methodology and the functionality of the computational implementation have been identified, including; the development of more advanced modular clustering criterions, the introduction of constraints and constraint management, and the development of module costing mechanisms/metrics.