What is the effect of deliberation on political actors and when can we expect it to be successful? Are mutual understanding and consensus realistic results of political decision-making processes or is compromise the most we can hope for? This book addresses what appear to be blind spots in theories of deliberative democracy: the conceptual and empirical relationship between communication and political preferences and the institutional preconditions for preference change and co-ordination. It proposes a model of preference transformation through communication and develops a typology of modes of political interaction that distinguishes discussion, deliberation, debate and bargaining. This serves as a framework for the analysis of a fundamental and highly polarizing conflict - the German decision over the import of embryonic stem cells. Analysis of communicative interaction in different forums shows how a well justified and widely accepted compromise was achieved in a conflict that had appeared irresolvable in moral terms and irreducible in terms of interest.