It is a well-known fact that it is in the early phases of production system design where the most important decisions are made. If the production system is not designed in a proper way, this will eventually end up with disturbances and problems during serial production and it is in the early phases the potential to influence is greatest. The purpose with this paper is therefore to describe how to work and what activities to focus on in early phases of production system design by proposing a structured production system design model focusing on the early phases which can be applied by practitioners and academics. Six production system design projects were studied in three real-time case studies and three retrospective case studies. Combined with literature studies a production system design model is developed describing the initial phases of initiation, project definition and concept including activities and decision points.