This chapter introduces the 10 principles of economics. It establishes that economics studies how people make choices under scarcity. Resources are limited but needs and wants are not, so people must make tradeoffs. Rational decision making involves considering costs, like opportunity costs, and responding to incentives. Trade can make all parties better off through markets, though governments sometimes need to improve outcomes. A country's production ability determines living standards, while too much money printing causes inflation, and societies face short-run tradeoffs between inflation and unemployment.