Accountability can mean many things, but increasingly it is linked to quantification. This is true in many fields, including law. This review considers how the recent emphasis on quantitative accountability has influenced law and legal practices. Rather than offering a broad survey of quantitative techniques deployed in law, the article examines three legal contexts in which quantification has shaped how actors are held accountable: sentencing guidelines, cost-benefit analysis in regulation, and law school rankings. The conditions that promote rigorous quantification, its effects on professional discretion, relations of authority, and resistance are examined. The article suggests fruitful questions and strategies for analyzing more broadly the effects of quantification in law.