Fluid resuscitation is generally considered a fundamental aspect in managing critically ill patients because it is intended to help optimize cardiac output and enhance tissue perfusion [1]. However, determining the appropriate volume of fluids to administer can be challenging, as both under- and over-resuscitation can result in significant morbidity and mortality [[2], [3], [4]]. Fluid responsiveness, defined as the ability of a patient's cardiac output to increase in response to a fluid bolus, has become an important concept in guiding fluid therapy [5], both in spontaneously breathing [6] and mechanically ventilated patients [7]. This narrative review will discuss the various methods to predict fluid responsiveness in critically ill patients and their clinical applications. Although fluid responsiveness is an important concept, it is debatable whether it should be solely used to manage fluid therapy in critically ill patients. Over the last year, new concepts have emerged assessing venous congestion [[8], [9], [10]].