Critical care medicine has been shaped by a series of landmark randomized trials that established evidence-based strategies for managing life-threatening illnesses. This chapter reviews pivotal studies that transformed practice in acute respiratory distress syndrome, sepsis, fluid resuscitation, vasopressor use, renal replacement therapy, and metabolic control in the ICU. Trials such as ARDSNet and PROSEVA defined the standard of lung-protective ventilation and prone positioning in ARDS, while SEPSISPAM and VASST clarified optimal blood pressure targets and vasopressor selection in septic shock. Fluid management strategies were refined through FACTT and ALBIOS, whereas AKIKI informed timing of renal replacement therapy. CRASH-2 demonstrated the survival benefit of tranexamic acid in trauma, and HYPRESS narrowed the role of corticosteroids in sepsis. Finally, the NICE-SUGAR trial fundamentally reshaped glucose management in critical illness by demonstrating harm from intensive insulin therapy. Together, these studies provide the foundation of modern critical care, replacing physiologic assumptions with rigorous trial evidence and directly influencing international guidelines.