Book excerpt: The trend of measuring performances is global and pervasive. We all live in quantified societies, in which performances in an ever-growing array of fields–from education to health, work to credit, justice to consumption–are assessed and governed through quantitative techniques. While the disruption brought by the quantitative turn has been widely studied by social scientists, legal research on the issue is minimal. This book aims to fill the gap. The essays herein collected explore how performance measurements interact with the law in different regions and sectors, which legal effects they produce, and for whose benefit.