The Mental Capacity Act’s provisions for best interests decision continue to provoke debate concerning the values and principles underpinning substitute decision making. However, less frequently addressed is the equally pressing question of who makes decisions on behalf of adults assessed to lack capacity.  I will argue that the MCA’s provisions for health and social care decision making are historically and globally atypical in privileging decisions made by health and social care professionals over the individual’s family, and relying on highly informal decision making processes.  This has significant socio-political consequences and raises important human rights questions.  I will argue that it is as important to attend to who the person wishes (or would wish) to make decisions on their behalf, as their wishes and preferences in relation to the decision itself.