In the > 30 years since the New Jersey Supreme Court’s seminal opinion in the case of Karen Ann Quinlan, all 50 states and the District of Columbia have enacted legislation to recognize the legal right of competent adults to write advance directives. The purpose of advance directives is to provide direction for health-care decisions near the end of life, when the ravages of illness, disease, or injury have taken the ability to decide for one’s self. This article reviews the defining features of advance directives and the governing law, discusses some common practical concerns regarding the use and effectiveness of advance directives, and identifies several significant ethical-legal challenges for honoring advance directives at the bedside. With a primary focus on the health-care proxy, the anatomy of advance directives is analyzed under four general rubrics: formal requirements, decisional capacity and when the directive takes effect, rights and responsibilities of proxies and health-care providers, and the scope and limitations of decisions to forego life-sustaining treatment. There is much common ground among state laws, but particular legal provisions may vary from state to state. Physicians, nurses, social workers, and other health-care professionals should be familiar with the law of their home state.