This article, written by Josephine Bailey and Kate Faulkner, discusses the collection of library usage data at the Squire Law Library, an academic law library embedded in the Faculty of Law at the University of Cambridge. Two initiatives were employed to survey usage: firstly, regular headcounts of library users and secondly, occasional spot-checks of university cards. This article details the data that was collected and how it fits into a wider ethnographic approach to understanding how students and researchers use libraries. The article also discusses how the pilots have developed into long-term procedures, and how this has led to improvements to the delivery of the service.