Creative design concepts are often viewed as developing iteratively, with the design problem and solutions ‘co-evolving’ in a mutually adaptive manner. We report a study examining whether the co-evolution concept captures the creativity arising in collaborative, team-based design practice. The analysis revealed that co-evolution episodes occurred regularly and embodied various directional transitions between problem and solution spaces. Moreover, the team leader often initiated this co-evolution. Co-evolution episodes linked with other creative activities such as analogising and mental simulation and there was a clear association between co-evolution and expressions of epistemic uncertainty, suggesting that designers were dealing with considerable complexity and ambiguity. Our findings support the view that co-evolution is the ‘engine’ of creativity in collaborative design.