The present monograph puts together, in a single volume, a fairly comprehensive, up-to-date and detailed treatment of PID control for multivariable processes, from paring, gain and phase margins, to various design methods and applications. The multivariable interactions are always a key issue and addressed explicitly and effectively. Both decentralized and centralized forms of PID controllers are discussed. Only knowledge of the linear control theory is assumed from readers. Illustrative examples of different degrees of complexity are given to facilitate understanding. Therefore, it is believed that the book can be accessed by graduate students, researchers and practicing engineers. This text is the first one solely focused on PID control for multivariable processes.