The scope of criminal justice surveillance, from the police to the prisons, has expanded rapidly in recent decades. At the same time, the use of big data has spread across a range of fields, including finance, politics, health, and criminal justice. Drawing on fieldwork conducted within the Los Angeles Police Department, Brayne shows how law enforcement uses predictive analytics and new surveillance technologies to allocate resources, identify criminal suspects, and conduct investigations. She then analyzes how the adoption of big data analytics transforms organizational practices, and how the police themselves respond to these new data-driven strategies. Proponents argue that big data can be used to make law enforcement practices more effective, fair, accountable, and objective, in part by stripping discretion from biased front-line actors. This research reveals the ways that police use of big data does not eliminate discretion, but rather displaces discretionary power to earlier, less visible parts of the policing process.