Article 12 of the United Nations Convention on the Rights of Persons with Disabilities, as interpreted by the Committee on the Rights of Persons with Disabilities in General Comment No. 1, offers a vision for law’s response to capacity impairments which differs in crucial ways from that contained in the Mental Capacity Act 2005. The Committee rejects the functional test for capacity and requires that a ‘will and preferences’ paradigm must replace the ‘best interests’ paradigm and that all substitute decision-making regimes must be abolished. This article draws on the position adopted in General Comment No. 1 in evaluating the best interests standard in the Mental Capacity Act. It sets out the normative case for a stronger legislative endorsement of will and preferences and the inclusion of greater support mechanisms but rejects the contention that all substitute decision-making can, or should, be abolished. It also argues that the best interests standard in the Mental Capacity Act retains some revolutionary potential and that, pending legislative reform, this can be further developed through the courts.