Optimization of the use of energy is of fundamental importance, particularly in view of the increasing tensions the world now faces between energy supply and demand. Chemical processes in general, and distillation processes in particular, account for a significant fraction of the world's energy usage. For example, distillation processes account for around 3% of the energy utilization in the US. There is thus a significant incentive to design systems so that energy utilization is minimized. Much progress has been made by the application of simple methods such as pinch technology (see for instance B. Linnhoff and R. Smith, Heat Exchanger Design Handbook, Begell House), but the problems encountered in complex distillation systems are such that a much higher level approach is needed. Authors Michael Georgiadis and Efstratios Pistikopoulos are from the Centre for Process Systems Engineering (CPSE) at Imperial College. CPSE is an international leader in the areas of process simulation, optimization and control. The application of techniques of the type described in this volume will make an important contribution to making the best use of mankind's increasingly scarce energy resources.