We discuss the representation of knowledge and of belief from the viewpoint of decision theory. While the Bayesian approach enjoys general-purpose applicability and axiomatic foundations, it suffers from several drawbacks. In particular, it does not model the belief formation process, and does not relate beliefs to evidence. We survey alternative approaches, and focus on formal model of casebased prediction and case-based decisions. A formal model of belief and knowledge representation needs to address several questions. The most basic ones are: (i) how do we represent knowledge? (ii) how do we represent beliefs? (iii) how is belief updated in light of new evidence? Decision and economic theory pose additional questions. First, how are knowledge and belief reflected in decision making? Second, can one derive the model axiomatically? That is, can we characterize the model by a set of conditions on observable data, in a way that would provide an observable definition of theoretical cons...