Design and control of reactive distillation systems of ternary decomposition reactions with two different relative volatility rankings, IK <-> LK + HK and HK <-> LK + IK, have been explored. Systems with intermediate boiling reactant have a behavior that is similar to that of the quaternary system with intermediate boiling reactants, if not simpler. Systems with heavy reactant are quite different. Two possible flowsheets (two-column and one-column configurations) have been discussed. The two-column flowsheet is workable for a wide range of chemical equilibrium constants. The one-column configuration is feasible for systems with high chemical equilibrium constants. Economical comparisons reveal that the one-column configuration is preferred for systems with large equilibrium constants while the two-column configuration is more economical in the region of low equilibrium constants. For the control of nonlinear reactive distillation systems, fast measurement (temperature measurement) is essential for tight control. Control performance deteriorates if significant measurement delay is present. Thus, parallel cascade control offers an attractive alternative for the control of reactive distillation systems in an offset free manner.