Project Outcome was launched by the Public Library Association (PLA) and funded through the Bill & Melinda Gates Foundation’s Global Libraries Initiative. The aim of Project Outcome was to fulfill a growing need among public libraries to demonstrate their value in our communities—and the power they have to improve lives—by making accessible the tools and resources library staff need to collect and use outcome data effectively. Evidence from the initiative’s multi-year evaluation—designed and conducted by ORS Impact—showed that Project Outcome helped increase use of outcome data for planning, strategic decision-making, and advocacy efforts by public libraries. A Theory of Change outcome map, also developed by ORS Impact (and re-designed in this paper), helped inform PLA’s strategy and evaluation plan prior to implementation. We feel privileged to have taken part in telling the Project Outcome story.