Proton pump inhibitors (PPIs) have become a mainstay of therapy not only in the practice of gastroenterology, but also for general medicine and even for the general public. Recently, proton pump inhibitors have been associated with a number of potential complications including impaired vitamin and mineral absorption, altered drug metabolism and increased risk for infections. The outline for the basis for these reported risks are examined in this book, the current clinical evidence is discussed, and the authors offer insight into the likely clinical significance of each complication. Furthermore, the pathophysiology of acid secretion and inhibition, with a specific focus on the pharmacological principles surrounding the use of PPIs are reviewed. Relevant information on the management of acid-related disordered is provided for clinicians. Other chapters explore the current literature on potential complications associated with long-term PPI use, the benefits and risks of routine use of proton pump inhibitors in the intensive care unit (ICU), often associated with adverse events such as a significantly increased risk of infectious complications, and the use and misuse of proton pump inhibitors in the general population.