Capacity is the ability to make decisions. Autonomy in decision-making and being safeguarded against abuse and undue influence are fundamental human rights. This chapter will demonstrate how "good" capacity assessment can support these human rights. The assessment of capacity is a complex and highly specialized task, governed by principles of the presumption of capacity, that capacity is not diagnosis bound, and the need for individualized, task-, and situation-specific assessments. The clinician engaged to undertake a capacity assessment has a responsibility to act as gatekeeper, and sometimes advocate, for the actualization of human rights. Capacity assessment presents opportunities to identify strengths and weaknesses to inform and enable supported decisionmaking. It also provides opportunities and obligations to identify abuse. When people with disability such as mental illness are empowered to make the decisions they are capable of making, while protected from making the decisions they are incapable of making, human rights are supported. Such principles are universal, regardless of the jurisdictional variations in the laws that govern capacity and competency determinations internationally.