The multinational company Prysmian Group designs and manufactures power and telecom cables. At their facility in Delft, the Netherlands, sustainable design has become increasingly important driven by customer demand. This led to several improvements of their power cables, such as the use of a recyclable plastic. These improvements are technical solutions for a problem in today’s product supply chain. In this thesis research, it is investigated if the sustainable design strategy of Prysmian Group Delft could go beyond these technical product improvements. After all, in order to decouple human consumption from the consumption and pollution of natural resources, we should focus on innovating socio-technical systems, rather than single products. A field of research which aims to support designers to contribute to these system innovations is Transition Design. Different Transition Design frameworks have been developed, but using them in commercial environment proves to be challenging. Therefore, in this research, it is explored how Transition Design theory could be adapted into a design method suitable for Prysmian Group Delft. This method should support the company to change their sustainable design strategy from making incremental improvements on their products to developing product systems that contribute to system innovation.Through an iterative process, in which interviews, creative workshops and design trials were used, insights were gathered on what this design method should look like. The resulting design method, named Product System Design Method (PSDM), integrates the system approach used in Transition Design into the design process of Prysmian Group Delft. In total, six variations to Prysmian’s design process were developed which increasingly address more system elements. Simultaneously, possible designs that follow from the PSDM were developed. Six illustrative designs, each representing one of the design processes, are presented in this research. In order to be of use for Prysmian Group Delft, it was argued that the PSDM should result in designs that do not only contribute to system innovation but also create value for Prysmian Group Delft. Therefore, the six illustrative designs were qualitatively analysed on to what extent the designs meet this requirement. This evaluation shows the designs that included more system elements do create more long-term benefits for Prysmian Group and make a bigger contribution to system innovation. However, their implementation also requires more changes at Prysmian Group Delft. Overall, it was concluded that the PSDM and the developed illustrative product system designs are a first step in the integration of system thinking into the design strategy of Prysmian Group Delft. However, given the current business strategy of Prysmian Group, the implementation of the PSDM and the illustrative product system designs is currently not expected.