For many companies, “customized” means products that even the most sophisticated of product configuration tools cannot define in advance. Such products need an engineer-to-order operations environment (ETO). This study focuses on the engineering activities of companies adopting an ETO strategy. We observed that these environments are significantly heterogeneous and that this is likely to limit any potential generic applicability of strategies and practices. In this paper, therefore, a three steps methodological approach to support companies in developing a better understanding of their ETO environment is presented: assessment of product variety and customization, modelling of the ETO process, and measurement of operational performance. Findings from the application of the approach to three industrial partners are then summarized.