The Consumer Price Index (CPI) is a measure of the average change over time in the prices paid by urban consumers for a market basket of consumer goods and services. The CPI currently tracks the spending patterns of two population groups: all urban consumers and urban wage earners and clerical workers. For 64 years, the U.S. Bureau of Labor Statistics (BLS) tracked the buying habits of only one population group. BLS then made several refinements to the CPI, one of which included broadening the population group. This move sparked controversy and has had a lasting influence on the CPI. This Beyond the Numbers article briefly looks at the history and evolution of the CPI, explains the reasoning behind the creation of two main indexes, and describes the debate surrounding this development.