Our focus herein is on developing an effective taxonomy for the simultaneous and real-time management of supply and demand chains. More specifically, the taxonomy is developed in terms of its underpinning components and its research foci. From a components perspective, we first consider the value chain of supplier, manufacturer, assembler, retailer, and customer, and then develop a consistent set of definitions for supply and demand chains based on the location of the customer order penetration point. From a research perspective, we classify the methods that are employed in the management of these chains, based on whether supply and/or demand are flexible or fixed. Interestingly, our taxonomy highlights a very critical research area at which both supply and demand are flexible, thus manageable. Simultaneous management of supply and demand chains sets the stage for mass customization which is concerned with meeting the needs of an individualized customer market. Simultaneous and real-time management of supply and demand chains set the stage for real-time mass customization (e.g., wherein a tailor first laser scans an individual's upper torso and then delivers a uniquely fitted jacket within a reasonable period, while the individual is waiting). The benefits of real-time mass customization can not be over-stated as products and services become indistinguishable and are co-produced in real-time, resulting in an overwhelming economic advantage.