This is an Executive Summary of a full evaluation conducted for the Oak Foundation in 2015. The evaluation provided an external assessment of the impact of the Oak Foundation's climate and marine philanthropy from 2009 to 2014, and the effectiveness of the strategies, internal structures, and approaches deployed. The lessons learned are also intended to guide the formation of a new strategic framework to guide grant-making to 2020. Thus, this review was intended to not only reflect on past programming and the Oak Foundation's role in environmental philanthropy, but also to update the understanding of baseline conditions, highlight important trends, needs, and opportunities, and identify ways to increase impact. The evaluation method was centered on interviews, desktop research, and a document review. The scope was not comprehensive; it focused on grants and initiatives that were of most interest to Oak leadership, and that had not been subject to a recent in-depth project evaluation. This Executive Summary is intended for external audiences, and does not include the sections covering the Foundation's internal processes and operations.