Making concept decisions is a crucial activity for product-developing companies since these decisions have high impact on the subsequent development and launch of the product. Consequences of unsuccessful concept decisions can be severe, e.g. missing out on business opportunities or spending money on rework. This thesis investigates concept decision making in product development practice and contributes by enhancing the understanding of what is actually happening, the difficulties experienced in the process, and how to manage and improve concept decision making. Such enhanced understanding should serve as a basis when support methods for concept decision making are developed. In-depth studies have been conducted in a Swedish automotive company, focusing on the technical system level of the product. The concept decision process was found to be a web of interconnected activities, embedded in the concept development process, and with several actors on different hierarchical levels. An overarching challenge identified in concept decision making was to achieve compatibility before completeness, meaning that compatibility between product systems must be met before the system solutions are completely developed. In addition, a number of conflicts intrinsic in the process were revealed, pointing to underlying causes of the difficulties in managing concept decision making. These conflicts are omnipresent due to the product and organizational complexity and have to be handled by the product developers in their daily work. The thesis identifies key elements for improving an organization’s concept decision making: Create meta-knowledge and awareness regarding what influences the process and the actors in the process since there is a general lack of knowledge regarding one’s own and the organization’s decision-making processes; Ask questions to ensure that aspects, previously neglected, are considered; Provide visualizations to enhance understanding of both process and solutions; Provide vision as guidance in everyday decision making and trade-offs; and Ensure reflections since there is a need for actors in the process to reflect on the own decision-making process. In conclusion, a model to improve the concept decision making in practice is proposed. The model includes a set of proposed activities that are designed to address the previously identified challenges, and was developed in collaboration between researchers and practitioners. / QC 20111019