The reactive dividing-wall column (RDWC) combines a reactor and a dividing-wall column (DWC) in a single column shell. Lately, various reaction systems have been proposed for the RDWC, but only little general knowledge has been published on the RDWC so far. The fundamental mechanisms of the RDWC are analyzed and a profound process understanding is deduced based on principal aspects of reactive distillation and the DWC. Fields of application and insights into the key factors for an energy-efficient operation are systematically derived. A semi-shortcut method is proposed to determine the minimum vapor demand of the RDWC and its energy-saving mechanism is explained. Thereby, process engineers can evaluate already during the process synthesis whether the RDWC is a promising option. Furthermore, they can quantify the energy savings quickly and get an understanding of the key factors for an energy-efficient column design and operation.