This document summarizes key concepts of choice theory, including the production possibilities frontier (PPF) which shows the optimal combinations of goods an economy can produce, individual budget lines which show affordable combinations of goods, assumptions about preferences such as more being better and averages being preferred, indifference curves that model preferences, and how optimal choices are made by equalizing the marginal rate of substitution with relative prices based on the budget line. This leads to the derivation of demand curves and exploring the substitution and income effects of price changes.