Publisher Summary Differential equations (DEs) have been employed in the preliminary design of distillation columns. The properties of DEs have also been used to gain an understanding of the general behaviour of distillation systems. These approaches have, until now, only been applied to traditional distillation column configurations. There are however, potentially very exciting gains to be made in separation, by exploring alternative distillation configurations. This chapter discusses one of such configurations—a coupled column system. The behavior of distillation column sections can be approximated using differential equations. As a result of the equal liquid and vapor flows on either side of a coupled system, simple mass balance dictates that the difference vector remain constant throughout each column. The difference vectors of the columns have equal magnitude but opposite direction. Coupled column section profiles are described in the chapter with illustrations and figures.