Variation in clinical management has been associated with suboptimal outcomes and increased costs. Guidelines, protocols, and clinical pathways have evolved as a strategy to standardize care, principally by limiting variation, thereby reducing complications, decreasing length of stay and improving outcomes. However, the nature of critical care makes it difficult to conduct blinded, randomized, and controlled clinical trials, the specific type of science required for evidenced-based medicine and guideline development. Areas in which ICU-based guidelines have been successful include, among others, sedation and neuromuscular blockade use, ventilator management, antibiotic selection, and vascular surgical interventions.