This Article examines the theoretical and practical implications of the substituted judgment and best interest standards for decision making by guardians. After providing an overview of the current decision-making standards in guardianship statutes, the Article synthesizes theoretical debates about what these standards mean and whether they provide an effective paradigm for surrogate decision makers. The authors then use new survey data to offer conclusions about the degree to which the substituted judgment and best interest standards are understood and meaningfully applied by guardians.