Sustainability and the need to leave the world in a healthy state for future generations is attracting increased global attention. In response, a growing number of private and institutional asset owners are making their investment decisions based on non-financial as well as financial criteria. The role that impact investing can play in these investment choices has become an important part of the conversation. To meet the rising demand for impact investment opportunities, a number of asset managers are developing impact investment products. The purpose of this white paper is to provide a theoretical and practical background to the subject of impact investing, describing its characteristics, the challenges faced by impact investors and, importantly, how impact can be measured in practice.