Past research has theorised that high levels of individual cognitive complexity may result in heightened design thinking and creativity. The precise relationship, however, between cognitive complexity and creativity in design remains largely unexplored. This chapter develops two measures of cognitive complexity in design: content complexity and structural complexity. Using a combination of protocol analysis and linkography it demonstrates how these two can be measured and studied. This chapter uses two sets of protocol data developed from experiments in parametric design. The results demonstrate that (i) content complexity effectively captures individual differences in cognitive complexity, and (ii) structural complexity, represented by decile growth plots in linkographs, reveals evolving cognitive patterns throughout the design process. This method for measuring cognitive complexity contributes to advancing fundamental knowledge about design cognition and thinking.