The reform of German guardianship law coming into force in 2023 will remove the term “well-being” from the law. This is intended to emphasise that the legal guardian should be guided by the subjective wishes of the person rather than by an objective understanding of well-being. This article analyses the understanding of well-being underlying the reformed guardianship law in comparison to common conceptions of well-being in philosophy and medical ethics, aiming to promote interdisciplinary understanding between ethics and law. The justification for the reform emphasises that the law is based on a subjective understanding of well-being. However, this understanding does not correspond to philosophical subjective theories of well-being, according to which only things that a person desires can contribute to her well-being. In contrast, the guardianship law assumes that the fulfilment of certain wishes can lead to objective harm to the person and thus impair her well-being. Negative consequences for the objective well-being of a person are only relevant insofar as they indicate a limit to following current wishes that are based on a natural will and are not an expression of self-determination. While the term “well-being” is removed from reformed guardianship law, the law implicitly contains an understanding of well-being comparable to a hybrid conception of well-being from a medical ethics perspective. According to this conception, fulfilment of a person’s wishes generally contributes to her well-being, although certain objective criteria are also taken into consideration.