Fluid therapy is one of the most widely used and necessary therapies for critically ill patients and those who are not able to hydrate and feed themselves spontaneously. Fluid Therapy in dogs and cats summarizes the fundamentals for understanding the water and electrolyte requirements of critical patients, the types of fluids that can be administered, and the consequences that a decision may entail. This handbook is published at a particularly relevant time, with the recent developments in orthogonal polarization spectral imaging; the advancements in hemodynamics, which have made it possible to assess the real efficacy of therapy and the side effects fluids can produce if not provided correctly; and the evidence-based advances that have changed the way fluid therapy in both human and veterinary medicine is now provided, which is very different from how it had been performed over the past 30 years. An attempt has been made in this book to address the topics homogeneously, following a functional approach for readers. Every chapter ends with a clinical case, which is useful for putting into practice what has been explained in the text.