The acidity or basicity of a compound under various conditions is a crucial property for the action and detection of the compound as a drug, pollutant, or other active chemical agent. Thus, the ability to predict pKa values using theoretical methods is extremely useful. This book describes the insights that have been gained on the intrinsic and extrinsic features that influence a molecule¿s acidity and examines the computational methods developed to estimate acidity from a compound¿s molecular structure. It presents techniques for both general and specific applications.