Over the last several decades, consensus has developed that medical treatment decisions should be based on the values, goals, and preferences of the patient. Ethically, such an approach is supported by the principle of autonomy, which has a rich tradition in Western philosophy. In the intensive care unit (ICU), however, patients are frequently unable to directly exercise autonomous choice. Multiple tools and methods, including advance directives and surrogate decision-making, have been advanced in an attempt to extend individual autonomy into a future where the capacity for autonomous choice has been lost. Such attempts are severely constrained by philosophical and practical limitations. In opposition to the ascendancy of patient autonomy, the concept of medical futility has been introduced, attempting to define circumstances where patient preference is irrelevant to medical decision-making. Additionally, the respect accorded the concept of autonomy itself can be attacked as culture-specific. Medical decision-making in the ICU, then, rarely represents a straightforward exercise of patient choice. The limitations of autonomy in the ICU setting have required other methods for optimal decision-making that demand an active participation on the part of physicians. Surrogate decision-makers remain invaluable but not infallible, requiring physicians to make independent assessments of the best interests of patients. Shared decision-making, where physicians contribute medical expertise and judgment while surrogates provide an intimate understanding of the values and goals of the patient, offers a practical model for optimizing decisions in the ICU.