Traditional social sector and international development organizations have prioritized measuring the impacts of their work for decades. Understanding the ways in which they are bringing about change or helping people and communities has long been part of the traditional social sector ethos. The Global Impact Investing Network (GIIN) was founded by The Rockefeller Foundation to support the maturation and professionalization of impact investing. The GIIN was uniquely mandated to help standardize practice, raise awareness about, and develop tools and resources for impact investing--in an effort to advance the industry. A surge in the amount of private capital available to solve social problems is creating a demand for new, more meaningful kinds of data and evidence. There is now widespread recognition that the current way of measuring impact is inadequate. Today, a number of substantial efforts to strengthen the evidence base for impact investing are underway. Global organizations such as the Word Economic Forum, the Organization for Economic Cooperation and Development, Social Value International (2017), and United Nations Principles for Responsible Investment (n.d.) are leading the charge to improve evaluation and measurement and are making promising strides toward bridging the cooperation gap between investors and evaluators. Ultimately, proving the value proposition of impact investment--that social impacts can be realized alongside financial returns, will require more cross-disciplinary cooperation from impact investors and evaluators alike.