In today’s fast-paced industry where fight for market share is fierce and reaching the market ahead of competition imperative, product development is a target for lead-time reductions. In this context, in product development in stage-gate processes, decisions need to be made even though knowledge and information are scarce and flawed. The challenge is how to support the decisions that are made in light of uncertainty and ambiguity. The thesis moves from analysing the role of the stage-gate process within the aerospace industry. The stage-gate process was more than a decision making mechanism, and instead a mechanism that facilitated communication, discussion and knowledge sharing between team members, as well as supported knowledge creation and shaping of the boundaries between people’s different perceptions of the knowledge base. However, the communicative and negotiative function of the stage-gate was highly dependent on the ability of the participating individuals to reflect on the status and quality of the available knowledge assets used throughout the process. To make this reflective activity an explicit part of the stage-gate practice, this thesis proposes the application of a knowledge maturity concept at the gates to raise the decision makers’ awareness of the status of the knowledge assets handled at the decision point. The knowledge maturity concept considers three basic dimensions: input, method/tool and experience/expertise in assessing the knowledge base maturity. The scale is intended to act as a boundary object, facilitating the knowledge creation process by highlighting the current status of the knowledge base and making stakeholders aware of the nature of the project’s uncertainties and ambiguities. In the knowledge maturity concept, its purpose is to support design teams at the gates in taking appropriate action, mitigating risk and focusing their efforts on improving the knowledge assets where it is needed most, regarding the situation at hand and, finally, to make more confident decisions.The thesis was developed within the EU FP6 VIVACE (Value Improvement through a Virtual Aeronautical Collaborative Enterprise) and EU FP7 CRESCENDO (Collaborative and Robust Engineering using Simulation Capability Enabling Next Design Optimisation) projects, and within the Faste Laboratory, a VINNOVA Excellence Centre involving partners from the Swedish manufacturing industry.