First published in 1987. The theory that political obligation and authority are derived from the consent of citizens is commonly accepted in the history of Western political thought. It is expressed in the famous assertion of the American Declaration of Independence that governments derive 'their just powers from the consent of the governed' and in the constitutions of some Western powers. This book provides the first systematic and comprehensive restatement and defence of consent theory since the 19th Century. It distinguishes consent from contract theory, examines what the actual consent of citizens can consist in and what place it must have in liberal democratic theory. The consent theory's relationship with ethics is explored and the major objections to the theory are countered. The author points to some political reforms which would increase the proportion of citizens in liberal democracies whose consent places them under political obligation. The book provides an overview of the current state of the consent theory of political obligation and authority.