Health care decision making for patients without decisional capacity is ethically and legally challenging. Advance directives (living wills) have proved to be of limited usefulness in clinical practice. Therefore, academic attention should focus more on substitute decision making by the next of kin. In this article, we comparatively analyse the legal approaches to substitute medical decision making in England and Germany. Based on the current ethico-legal discourse in both countries, three aspects of substitute decision making will be highlighted: (1) Should there be a legally predefined order of relatives who serve as health care proxies? (2) What should be the respective roles and decisional powers of patient-appointed versus court-appointed substitute decision-makers? (3) Which criteria should be determined by law to guide substitute decision-makers?