The 2015 International Conference on Engineering Design (ICED15) will be the twentieth held since the conference series was inaugurated in 1981. The Design Society is an international society founded in 2001 to develop an understanding of all aspects of Design. This proceedings is a compilation of the 427 peer-reviewed and accepted papers submitted to ICED15. All the accepted papers are divided among the following 11 themes into separate volumes: Design for Life; Design Theory and Research Methodology, Design Processes; Design Organisation and Management; Design for X, Design to X; Design Methods and Tools - Part 1; Design Methods and Tools - Part 2; Product Modularisation, Product Architecture, Systems Engineering, Product Service Systems; Innovation and Creativity; User-Centred Design, Design of Socio-Technical Systems; Design Information and Knowledge Management; Human Behaviour in Design, Design Education.