The 21st century is bringing about vast changes in the demographics of the United States. Notably, the population is aging at a rapid rate, and incidence of chronic illness and dementia is increasing, the disability population is aging, the nature of medical choices is changing due to evolving medical technology, and health care delivery systems are becoming increasingly complex. These trends bring health care clinicians up starkly against a growing challenge: The rising tide of patients with diminished decisional capacity.