Uncertainty is central to engineering design and new product development (NPD). While there has been substantial focus on dealing with uncertainty in technical systems and design information, how engineering designers react to and manage uncertainty is also critical to performance. However, an important gap remains in understanding what activities NPD teams engage in based on the specific uncertainty types they face. This gap is investigated via a conceptual framework detailing four uncertainty types (technical, organisational, resource and market) and three project activities (information, knowledge sharing and representation). Evidence is presented from two engineering design cases with 45 interviews, observations, and secondary data. Based on this, specific links are described between uncertainty type and project activity as follows: technical uncertainty drove representation activity, organisational uncertainty drove knowledge sharing activity, resource uncertainty drove knowledge sharing activity, and market uncertainty drove information activity. These findings are developed into a number of propositional relationships between the four uncertainty types and specific project activities, which form the basis for a number of implications for engineering design research and practice.