This book aims to define – or to re-define – anarchism in relation to the fundamental ethico-political problem of authority. Authority is defined in terms of the right to exercise social control (as explored in the ‘sociology of power’) and the correlative duty to obey (as explored in the ‘philosophy of practical reason’). Anarchism is distinguished, philosophically, by its scepticism towards such moral relations – by its questioning of the claims made for such normative power – and, practically, by its challenge to those ‘authoritative’ powers which cannot justify their claims and which are therefore deemed illegitimate or without moral foundation.