This book gives a practical in-depth account of the concept of control valve, its role as a dynamic element in the process, its types, sizing and selection. It explains the underlying issues that must be considered and the factors involved. It clarifies the ambiguities surrounding these factors and illustrates their relationships and interactions. The book explains how the control valve behavior changes, and its characteristics are modified, under the varying process conditions so that a prediction of valve behavior can be made prior to selection.