Book excerpt: Even though Computer Aided Design (CAD) tools have changed the way designers work in most parts of the design process, designers still mostly use pen-and-paper sketching when generating design ideas. Previous studies exploring the use of CAD tools for design ideation have concluded that the tools available at the time did not support reflective conversation, serendipitous interpretation and creativity, making them unsuited for design ideation. However, many of these studies used tools now considered obsolete, implying that the conclusions might no longer be valid. With the variety and capabilities of current CAD tools, there is an opportunity for a new exploration of CAD tools in design ideation. The aim of this licentiate thesis was to explore the use of CAD tools as externalization media in design ideation, what effect this has on the ideation process and how CAD tools might support design ideation. To this end, the thesis explored the use of CAD tools in design ideation in four studies. The first study consisted of a literature review on the strengths and weaknesses of sketches and CAD tools and a focus group discussion with three design experts. The second study compared master theses to explore how design representations used in the design process affect the breadth of design space exploration. The third study was a case study with two cases featuring the use of game engines and Virtual Reality for automotive lighting design and the fourth study compared the workflow in VR-sketching and pen-and- paper sketching. The results of the studies in this thesis suggest that the notion that CAD tools are not useful for design ideation is no longer true. Based on expert evaluations and case studies, this thesis concludes that there are several opportunities for the use of CAD tools in design ideation. This is certainly true in design fields where it is difficult to make sketches. The potential strengths of using CAD tools for design ideation includes the ability to design in full scale and the ability to perform instantaneous transform operations, such as scaling and deforming. However, the ability to instantly undo in CAD tools has been identified as both a potential strength and potential a weakness for design ideation. While being able to rapidly undo mistakes could be beneficial to the ideation process, achieving a faster workflow with less time redoing and more time working on creating, this might also result in fewer opportunities for reinterpretation. The conclusions in this thesis provide arguments for the use of CAD tools in design ideation, which could lead to new ways of generating, working with and thinking about design ideas. The findings also act as a stepping stone for further studies in the area of Computer Aided Ideation.