Sales and Operations Planning (S&OP) is the process through which enterprises develop tactical plans for aligning supply and demand management activities, usually with the objective of maximizing profitability. Demand-supply balancing is particularly complex and challenging in Engineer-to-Order (ETO) manufacturing environments, which are characterized by highly customer-driven order-fulfilment processes, creating a dynamic and uncertain planning environment. Recent studies highlight that ETO environments and their contextual influence on S&OP have been overlooked within extant S&OP research. This paper addresses this by investigating how the characteristics of ETO manufacturing influence the design of S&OP. Through a case study of a maritime equipment manufacturer, the paper identifies requirements that are imposed on the S&OP process by the characteristics of an ETO planning environment. These requirements serve as basis for identifying three main research areas that can support the design of S&OP in ETO environments, namely, customer enquiry management, multi-project management and spare parts management. The findings are summarized in a high-level framework for S&OP in ETO production and related research areas.