In manufacturing companies a gap between theory and practice concerning systematic design and evaluation of assembly systems is discerned. In this paper a number of questions are raised to enhance the understanding of the associated problems in order to reduce the gap. The assembly system design and evaluation process is considered as a means to achieve the goal, a successful assembly system. The relation between how companies work with assembly system design and evaluation and some decisive circumstances are identified. The questions are discussed outgoing from empirical results. Potentials for improvements in design and evaluation of assembly systems are identified.