The adoption of barcode scanning technology in the 1970s gave rise to a new form of data: scanner data. Soon afterwards, researchers began using this new resource, and since then a large number of papers have exploited scanner data. The data provide detailed price, quantity, and product characteristic information for completely disaggregate products at high frequency, and they typically track a panel of stores and/or consumers. Their availability has led to advances, inter alia, in the study of consumer demand, the measurement of market power, firms’ strategic interactions and decision making, the evaluation of policy reforms, and the measurement of price dispersion and inflation. In this article we highlight some of the pros and cons of this data source, and we discuss some of the ways its availability to researchers has transformed the economics literature.