Volume management is an integral component of the care of critically ill patients to maintain hemodynamic stability and optimize organ function. The dynamic nature of critical illness often necessitates volume resuscitation and contributes to fluid overload particularly in the presence of altered renal function. Diuretics are commonly used as an initial therapy to increase urine output; however they have limited effectiveness due to underlying acute kidney injury and other factors contributing to diuretic resistance. Continuous renal replacement techniques (CRRT) are often required for volume management. In this setting, successful volume management depends on an accurate assessment of fluid status, an adequate comprehension of the principles of fluid management with ultrafiltration, and clear treatment goals. Complications related to excessive ultrafiltration can occur and have serious consequences. A careful monitoring of fluid balance is therefore essential for all patients. This review provides an overview of the appropriate assessment and management of volume status in critically ill patients and its management with CRRT to optimize organ function and prevent complications of fluid overload.