The best-interests standard was introduced to undercut policies that children (and other incompetent persons) were property of their guardians and to give children's interests some weight. Judges, physicians, lawmakers, teachers, and others increasingly used it as a guide for making decisions for persons lacking decision-making capacity. The best-interests standard has been discussed frequently in the medical, legal, and bioethics literature, but it is given different meanings by different authors. The chapter argues that the best-interests standard should be adopted for persons of all ages for reasons of consistency, compassion, and justice and that there should not be one rule for infants and another for the rest of us. Unlike Child Abuse Protection and Treatment Act (CAPTA's) Baby Doe rules, the best-interests standard permits, within morally, legally, and socially sanctioned limits and established duties, the sort of compassionate and individualized medical decision making adults want for themselves.