Amid rampant investor demand, the market for ESG data is set to top $750 million in 2020—over triple 2015 sales; ESG data providers cover a wide range of regions, sectors, and asset classes, and use differing methodologies and definitions; We note three overlapping categories of ESG data providers: market, ESG-exclusive, and specialized (e.g. climate); In the absence of mandatory disclosure, reported ESG data points vary substantially across countries and firms; Given still-patchy data availability, there is little correlation among ESG scores from different providers