This article aims to give readers an overview of the Mental Capacity Act 2005 and its role in supporting the right to autonomy of people who, because of their disability, may unreasonably and unjustifiably be excluded from decisions with which they should and can be involved. The article also considers situations in which people need support in making decisions and how such support can be given. Finally, it outlines the principles to be followed when making a decision on behalf of a person who lacks capacity.