Is philanthropy less than the sum of its parts? We know of countless examples of individual organizational excellence: nonprofits and foundations that achieve extraordinary impact on the great challenges of our time. But it is hard to avoid the haunting sense that all this good work does not add up. The efforts of individual organizations are fragmented and isolated. This fragmentation yields real challenges: inefficient fundraising, infrequent collaboration, and uneven learning. All told, it is difficult to articulate the impact of the whole of philanthropy. Over the last few decades a new science has emerged that wrestles with the questions of systems-level behavior. The philanthropic community can learn much from this work. This paper is an initial effort to connect the insights from complex systems science with nonprofits, foundations, and all those devoted to making a better world.