This book deals with economic theory, not methodology. It does employ certain methodological resolutions. These resolutions and the limitations they impose on the nature and the scope of the analysis are reviewed. The first resolution concerns what kind of a theory is to be discussed. The word theory may mean many things; it may mean a hypothesis put forward as an explanation of something, an idea, or a notion. In a normative sense it may mean a recommendation, a rule, or principle to be followed. In science it usually means a system of hypotheses to be accepted as an explanation of certain facts, a set of general laws, and principles. It is also used to distinguish the general principles and methods of a subject from the practice of it. The theory with which this volume is concerned is that of science. In very general terms it may be defined as a system of hypotheses, one following from another, which permits the reader to derive from known facts and predictions of other facts. If the knowledge of the fact which we predict is important for us, in the sense that it permits us to achieve better the objectives we pursue, the theory may have a practical value. This book is therefore not only a contribution to the analysis of expectations but also an introduction to a number of selected topics in economic theory.