This document provides a framework for developing a performance measurement system for libraries. It begins by outlining key underlying assumptions, such as the difficulty of establishing a "culture of assessment" in libraries. It then presents a multi-step framework for defining and implementing meaningful performance measures. The steps include understanding the context, aligning strategies and objectives, identifying services and programs, defining measures, managing measurement data, translating data into outcomes and impacts, and communicating results. Examples are provided for each step to illustrate how to apply the framework. The overall goal is to select measures that demonstrate the library's impact and value to its stakeholders.