The Consumer Price Index (CPI) is a measure of the average change over time in the prices paid by consumers for a basket of consumer goods and services. It is a widely used indicator for tracking changes in the overall cost of living and is a key economic indicator that helps assess inflation and purchasing power. The CPI is directly relevant to the topics of 19.2 Adjusting Nominal Values to Real Values, 19.4 Comparing GDP among Countries, 22.2 How to Measure Changes in the Cost of Living, 22.3 How the U.S. and Other Countries Experience Inflation, and 22.5 Indexing and Its Limitations. It serves as a crucial tool for understanding the real purchasing power of consumers, comparing economic performance across countries, and tracking the impact of inflation on the cost of living.