A novel materials selection procedure has been developed and implemented in software. The procedure uses Materials Selection Charts and performance indices to select materials and shapes for mechanical design. Performance indices are combinations of material properties that govern performance. Optimization methods are used to simultaneously select material and shape. The performance index for a light, stiff beam is E^½/ρ, where E is Young's modulus and ρ is density. This index is used to select materials for components where performance depends on a combination of properties. The cross-section shape can also be included in the performance index by introducing a shape factor, φ. The new performance index, M₂, incorporates this shape factor and is given by √(φE)/ρ. Material selection charts are used to plot material properties on axes, allowing the identification of materials with high values of performance indices. These charts include logarithmic scales to cover a wide range of materials. The Cambridge Materials Selector (CMS) software is used to perform material selection, with a database of material properties, a management system, and a graphical user interface. The CMS allows users to perform multiple selection stages, each with a pair of material properties. The results of each stage can be stored and reviewed. The software also includes data manipulation routines for zooming, listing properties, and plotting graphs. In case studies, the CMS is used to select materials for oars and precision instruments. For oars, materials like wood and carbon-fibre reinforced polymers (CFRP) are recommended. For precision instruments, materials with high thermal conductivity and low expansion coefficient, such as silicon and silicon carbide, are recommended. The software provides a database of materials with a wide range of properties, including mechanical, thermal, and electrical properties. It also includes information on environmental performance, processing, and typical uses. The CMS is a powerful tool for mechanical design, enabling the selection of materials with optimal properties and shapes.A novel materials selection procedure has been developed and implemented in software. The procedure uses Materials Selection Charts and performance indices to select materials and shapes for mechanical design. Performance indices are combinations of material properties that govern performance. Optimization methods are used to simultaneously select material and shape. The performance index for a light, stiff beam is E^½/ρ, where E is Young's modulus and ρ is density. This index is used to select materials for components where performance depends on a combination of properties. The cross-section shape can also be included in the performance index by introducing a shape factor, φ. The new performance index, M₂, incorporates this shape factor and is given by √(φE)/ρ. Material selection charts are used to plot material properties on axes, allowing the identification of materials with high values of performance indices. These charts include logarithmic scales to cover a wide range of materials. The Cambridge Materials Selector (CMS) software is used to perform material selection, with a database of material properties, a management system, and a graphical user interface. The CMS allows users to perform multiple selection stages, each with a pair of material properties. The results of each stage can be stored and reviewed. The software also includes data manipulation routines for zooming, listing properties, and plotting graphs. In case studies, the CMS is used to select materials for oars and precision instruments. For oars, materials like wood and carbon-fibre reinforced polymers (CFRP) are recommended. For precision instruments, materials with high thermal conductivity and low expansion coefficient, such as silicon and silicon carbide, are recommended. The software provides a database of materials with a wide range of properties, including mechanical, thermal, and electrical properties. It also includes information on environmental performance, processing, and typical uses. The CMS is a powerful tool for mechanical design, enabling the selection of materials with optimal properties and shapes.