Here is a collection of sources which might be useful to anyone who wishes to learn more about the field of impact investing:
Global Impact Investing Network: The Global Impact Investing Network (GIIN) is the global champion of impact investing, dedicated to increasing its scale and effectiveness around the world.
Impact Alpha: ImpactAlpha is a digital media company redefining business journalism around social and environmental value.
UN Sustainable Development Goals: The Sustainable Development Goals are a collection of 17 global goals designed to be a "blueprint to achieve a better and more sustainable future for all".
Impact Management Project: The Impact Management Project (IMP) is a forum for organisations to build consensus on how to measure, compare and report impacts on environmental and social issues.
Global Steering Group for Impact Investment: The Global Steering Group for Impact Investment (GSG) is an independent global steering group catalyzing impact investment and entrepreneurship to benefit people and planet.
“Impact investing : instruments, mechanisms and actors” by Wolfgang Spiess-Knafl and Barbara Scheck