Intravenous administration of fluids is perhaps the most common treatment provided in the hospitals for various indications. Fluids may be used for maintenance, concurrent replacement and deficit replacement. Understanding of certain basic principles relating to the body composition, behaviour of fluids and electrolytes in the body and composition of available intravenous fluids is a basic prerequisite. Parenteral fluid administration can be life-saving; however, if used incorrectly it can lead to development of avoidable complications such as iatrogenic hyponatremia and cerebral oedema. Type of fluid administered varies with the condition of the patient. Each situation demands an individualized approach with proper assessment and monitoring- clinical signs and laboratory tests. Updated education on intravenous fluid prescription is needed. This article discusses the basic physiology and evolution of our understanding of fluid administration and consensus regarding fluid administration as maintenance therapy and in certain commonly faced situations.