This book collects all the papers that appeared in 2005 in Kno- edge, Rationality and Action (KRA), a journal published as a s- cial section of Synthese, which addresses contemporary issues in epistemic logic, belief revision, game and decision theory, rational agency, planning and theories of action. As such, the special section appeals to researchers from Computer Science, Game Theory, Ar- ?cial Intelligence, Philosophy, Knowledge Representation, Logic and Agents, addressing issues in arti?cial systems that have to gather information, reason about it and then make a sensible decision about what to do next. It will be clear already from the contents pages, that this book indeed re?ects the core of KRA: the papers in this volume address degrees of belief or certainty, and rational agency. The latter has several manifestations: often constraints on the agent’s belief, behaviour or decision making. Moreover, this book shows that KRA indeed represents a ‘loop’ in the behaviour of the agent: after having made a decision, the life of the agent does not end, rather, it will do some sensing or collect otherwise the outcome of its decision, to update its beliefs or knowledge accordingly and make up its mind about the next decision task.