In today’s world of multi-component and multi-technology products, firms are obliged to seek knowledge for new product development (NPD) from external sources. Supplier firms are one such external source. The thesis aims to contribute to the development of a theory on supplier involvement in new product development (NPD) by advancing understanding of the motives and conditions for the utilization of supplier information and knowledge in the fuzzy front end (FFE) of NPD. The term ‘fuzzy front end’ (FFE) refers to the activities that the firm undertakes prior to a NPD project. The FFE ends when the NPD project is launched, or rejected. The FFE of NPD is information intensive: it requires seeking, accessing and selecting different types of information from both internal and external sources. Previous research focused mostly on the external source of consumers and how ideas from consumers can lead to the generation of new product concepts. By comparison, the suppliers’ contribution to the FFE of NPD has received less attention. The thesis examines the exchange and utilization of supplier information and knowledge at the micro-social level of the firm between the individuals who work in the FFE of NPD. Three functional areas have been selected for the study, namely: (Design) Engineering and Purchasing of the customer firm and Sales Engineering of the supplier firm.