Gross national product is a familiar measure of the size of an economy, and the change in GNP is a familiar measure of the rate of economic growth. But decisions about what to include in GNP and how to value those components turn on how economic activity is conceptualized by the social scientists and statisticians responsible for constructing the measure. Macekura traces the genesis and trajectory of the idea over the course of the twentieth century. He shows how the invention of GNP encouraged a focus on aggregate economic growth as the objective of economic policy and describes the long line of skeptics who have criticized GNP for neglecting nonmarket work, ignoring the distribution of income, failing to account for resource depletion and environmental degradation, and focusing on output rather than human welfare or happiness. The reader comes away persuaded that GNP, although an imperfect summary indicator of the state of an economy, plays an outsize role in contemporary conceptions of economic policy and performance.