It is a well known fact that prolonged exercise during sports training and competition leads to various disturbances which culminates in dehydration. Dehydration is commonly observed during physical activity which can be elicited within an hour of exercise especially if athletes enter the exercise session dehydrated. The onset of dehydration is preventable or atleast modifiable when hydration protocols are followed that will ensure voluntary euhydration by the athletes. Therefore, appropriate drinking practices that include fluid, electrolyte, and substrate needs before, during, and after a period of exercise is important. This book aims to highlight the different fluid compartments of the body along with the disturbances that take place in human body as a result of dehydration. It also focuses on the importance of rehydration and basics of rehydration including the role and content of replacement beverages required. It has also been observed that the knowledge and practices related to hydration is highly lacking in athletes, therefore a small effort has been made in this book to address few important issues and the essentials of drinking to be kept in mind for adequate hydration