This chapter explores the ways that private media companies take users’ personal data as a proxy for public life, and discusses the consequences this development poses for public knowledge. In contrast to sweeping claims about the efficacy of data analytics, Melissa Aronczyk argues that the data these companies collect are often relevant only to specific behaviors carried out in a predetermined context. They reflect a system engineered to maximize attention and profit while adhering to security and privacy regulations. The resulting data set thus are highly specific to the conditions in which they are produced and cannot stand in for any more general public opinion. Aronczyk discusses the United Nations’ use of datasets donated by private companies to address their agenda for climate mitigation, and questions the reliability of that data for making inferences about human behavior. More broadly, she interrogates the wisdom of taking our cues from corporations by adopting the same assumption they make about what their data means.