The objective of this consensus-based S1 Guideline for perioperative fluid therapy in children is to maintain or re-establish the child's homeostasis. Therefore, the perioperative fasting times should be as short as possible to prevent patient discomfort, dehydration, and ketoacidosis. For the intraoperative background infusion a physiologically composed balanced isotonic electrolyte solution (BS) with 1 - 2.5% glucose is recommended to maintain normal glucose concentrations and to avoid hyponatremia, hyperchloremia, and lipolysis. Additional BS without glucose can be used in patients with circulatory instability until the desired effect is achieved. The additional use of colloids is recommended to recover normovolemia and to avoid fluid overload when crystalloids alone are not sufficient and blood products are not indicated. Monitoring should be extended in cases with major surgery.