Design evaluation is characterized by its subjective nature. People with minimal or no design expertise may have different expectations and perceptions of design. A primary goal of this dissertation is to investigate expertise-related effects on the evaluation of design products using different methods. Two literature reviews and three empirical research articles are presented as independent chapters in this “papers option” dissertation.Chapter 2 presents a literature review on the nature of expertise and expert performance and summarizes how design researchers have investigated the role of expertise in design process. Previous design studies often adopted the experience/knowledge-based view of expertise. Chapter 3 presents a review of literature on neurocognitive measures applied to design research studies, including design evaluation studies. The application of neuroscience methods to testing and evaluating design solutions shows great potential for design practices in various fields. Chapter 4 reports two studies investigating the effect of design expertise on the evaluation of lamp designs using the consensual assessment technique, a well-validated tool for evaluating creative products. Results showed that the effect of expertise level on evaluation outcomes varies depending upon the design being evaluated. Experts, quasi-experts, and novices appear to rate and rank some designs similarly high or low, but not all. Chapter 5 describes an eye-tracking study investigating whether there are differences in the gaze behavior of experts, quasi-experts, and novices when evaluating the same set of designs as for the Chapter 4 studies. The results provided partial support for the hypothesized classical expert gaze behavior (i.e., fewer fixations of longer durations) identified by previous researchers in non-design fields. This study provides empirical evidence for the impact of design expertise on visual exploration and design judgment. Chapter 6 presents a mixed methods study exploring gaze behavior, criteria-based evaluations indicating perceived design quality, and the thought process underlying design evaluation. Results showed that as the total time fixating on a design increases, the functionality rating of this design decreases. Different aspects of design quality have unequal impacts on the overall evaluation of design. Plausible explanations for the perceived design quality are identified through interview. Overall, the research findings provide implications for design evaluation and contribute insights into design expertise and education.