Reviewers tell us that Case/Fair is one of the all-time bestselling principles of economics texts because they trust it to be clear, thorough and complete. This well-respected author team is joined for the 9th edition by a new co-author, Sharon Oster. Sharon's research and teaching experience brings new coverage of modern topics and an applied approach to economic theory, as demonstrated in the new Economics in Practice feature. Introduction to Economics; The Market System: Choices Made by Households and Firms; Market Imperfections and the Role of Government; Concepts and Problems in Macroeconomics; The Core of Macroeconomic Theory; Further Macroeconomic Issues; The World Economy Case/Fair/Oster, believe that the best way to understand how market opportunities operate and the best way to understand basic economic theory is to work through the perfectly competitive model first, including discussions of output markets and input markets, and the connections between them, before turning to noncompetitive market structures, such as monopoly and oligopoly.