In today's competitive and turbulent environment companies engaged in new product development (NPD) need to have a sophisticated understanding of the types of knowledge critical to the each phase of the NPD process. This types of knowledge is used in so-called "stage-gate" NPD processes. This work will describe a typical NPD stage-gate process and indicate the critical knowledge types needed at the different stages. The identification of the critical knowledge used at each stage was done by combining knowledge of the literature and practical experience of running NPD processes in an industrial setting. The different types of knowledge required at different stages of the development process will be described and elaborated on. When providing knowledge management systems to support the NPD process, one needs to consider providing a system that can cater for knowledge that may take Different forms. This research contributes to our understanding of the nature of those knowledge forms.