'Deliberative politics' refers to the role of conversation and arguments in politics. Until recently discussion of deliberative politics took place almost exclusively among political philosophers, but many questions raised in this philosophical discussion cry out for empirical investigation. This book provides the first extended empirical study of deliberative politics, addressing, in particular, questions of the preconditions and consequences of high level deliberation. Using parliamentary debates in Germany, Switzerland, the United Kingdom and the United States as an empirical base, the authors measure the level of deliberation by constructing a 'Discourse Quality Index'. As deliberative politics moves to the forefront of political theory, this book makes an important contribution to deliberative democracy.