This document discusses the future of library performance measurement in the UK higher education system. It notes that government now requires a Teaching Excellence Framework to measure universities' contributions to teaching, and libraries should provide compelling measures of how they contribute to teaching excellence, preferably using big data. However, libraries remain complex organizations with collections, services, spaces and partnerships that define their distinctiveness. Effective performance measurement requires understanding libraries as dynamic social systems, using operational data for continuous improvement while also demonstrating value through scorecards and cultural leadership.