Fundamental and complex questions surround discrimination law and plague its application. When is discrimination justifiable? What is the purpose of the law, and its relationship to social equality? Is discrimination law designed to protect individual choices or marginalised groups? This book presents a unified theory of discrimination law, arguing that these questions have remained controversial because of a failure to distinguish between the need to justify the practise of discrimination law, from the need to justify the duty imposing rules of this practise. The book argues that the law is grounded not in the value of equality but autonomy - its purpose to provide people with a free choice between valuable options. It presents discrimination law as a distinctively liberal social programme.