Product development projects need to be managed in a timely and efficient manner in the present competitive business environment. The authors of this work argue that the commonly used product development models do not fully meet this demand, and the decision-making process needs to be made explicit. This work mainly focuses on the product development process. Two companies were studied using case study research. The aim of the case study was to identify key factors affecting the decision-making process in product development. The type of collaboration used in these two companies was also investigated in order to identify the influence it had on the decision-making process of each. The two companies had different views of the decision-making process which were related to their level of development process knowledge. Common factors affecting the decision-making process in product development were divided into ten categories: (1) Handling of requirements, (2) Experience of projects, (3) Organizational aspects, (4) Project management, (5) Top management, (6) Knowledge, (7) Risk management, (8) Information systems, (9) Communication, and (10) Change management.