For 1-Semester Principles of Microeconomics courses. This Principles of Microeconomics text uses 5 key principles, and an Active Approach to teach microeconomics. O'Sullivan/Sheffrin makes use of Active Learning Tools which get students involved in role-playing, help them apply concepts, and offer reinforcement of the material (tools include: Economic Experiments, Application Questions, and Test Your Understanding Questions). The text provides a clear, concise, and accessible presentation of key points. Its hallmark feature includes a focus on the 5 Key Principles of Economics--1) Opportunity Cost, 2) The Marginal Principle (comparing marginal benefits and marginal costs), 3) Diminishing Returns, 4) The Principle of Voluntary Exchange, 5) The Real-Nominal Principle (distinguishing real from nominal magnitudes). It is available in a hardbound, Economics text, as well as, Micro and Macro splits.