Impact investing has grown significantly over the past 15 years. From a niche investing segment with only $25 billion AUM in 2013 (WEF 2013), it experienced double-digit growth and developed into a market with an estimated $502 billion AUM (Mudaliapar and Dithrich 2019). Despite the growth and maturation of impact investing, gathering complete and accurate data on the characteristics of this industry continues to be a challenge. This paper describes the creation of a new dataset on both impact investors and the portfolio companies they fund, comprising 445 impact investors and 14,165 portfolio companies. We code impact investors according to established categories such as legal form, types of investments and return objectives. We then develop measures of the relative importance of social impact for each investor in an effort to add a new analytic categorization. We conclude by describing the distribution of investors and firms across these various categories.