Oliguria, commonly defined as a urine output (UO) of less than 0.5 mL/kg/h over a period of 6 h, is a frequent clinical concern in the intensive care unit (ICU). However, recent evidence suggests that lower thresholds, such as UO less than 0.3 mL/kg/h, may be more predictive of acute kidney injury (AKI) in perioperative and critically ill patients. Oliguria can represent either a physiological response to various stimuli or a pathological process indicating decreased renal perfusion or injury. Distinguishing between physiological and pathological oliguria is essential to guide appropriate interventions and avoid potential harm from unnecessary treatments. This chapter provides a comprehensive approach to assessing and managing oliguria in the ICU, incorporating current guidelines and evidence-based practices [1] [Ref: Algorithm 20.1].