In the area process control, new methods of analysis and synthesis of control systems have been developed and need to be added to the process control engineer's bag of practical methods. The driving force for much of this development was the drastic increase in energy costs in the 1970's . This led to major redesigns of many new and old processes, using energy integration and more complex processing schemes. The resulting plants are more interconnected. This increases control loop interactions and expands the dimension of control problems. There are many important processes in which three, four, or even more control loops interact.

As a result, there has been a lot of research activity in multivariable control, both in academia and in industry. Some practical, useful tools have been developed to design control systems for these multivariable processes. The second edition includes a fairly comprehensive discussion of what I feel are the useful techniques for controlling multivariable processes.