摘要:As its seven-year Nuclear Security Initiative wound down in late 2014, the William and Flora Hewlett Foundation engaged ORS Impact to conduct a summative evaluation. That evaluation yielded insights pertinent to future work on nuclear security and other fields where policy-related investments, strategies, and goals are prioritized, as well as insights regarding Hewlett’s approach to the initiative exit. During the life of the initiative, significant changes in the geopolitical landscape influenced both the relevance and the expected pace of advancement of its established goals and targets. Rather than focusing on whether identified targets had been achieved in a narrow “success/failure” framework, the evaluation explored where and how Hewlett’s investments and actions made a difference and where meaningful progress occurred over the seven years of investment. Evaluation findings highlighted contributions and areas of progress that had not been explicitly anticipated or specifically identified in the initiative’s theory of change. This article describes the initiative and its theory of change, evaluation methods and approaches, findings, and how these informed the foundation’s planning for initiative exits and approach to measurement of time-bound investments. Although time-bound philanthropic initiatives are a well-established practice, the approach merits closer examination in order to discern effective ways to implement, evaluate, and wind down these types of investments.