Investment research firm Morningstar has bought a 40% stake in Sustainalytics, a provider of environmental, social, and governance (ESG) research and ratings, for an undisclosed sum.

The recent move builds on a previous alliance between the two parties that dates back to August 2015 and led to the launch of the Morningstar Sustainability Rating for global mutual and exchange-traded funds (ETFs) in March 2016.

Morningstar CEO Kunal Kapoor said: “Enhancing this relationship enables us to leverage the expertise Sustainalytics has built over the last 25 years, and build on the momentum we started with the launch of the Sustainability Rating.

“We have the largest ESG fund coverage universe today, and we look forward to continuing to meet the increasingly sophisticated ESG needs and requirements of our clients through integrated solutions and innovative research that highlights good stewardship, lower costs, and transparency for investors.”

The deal involves the Sustainalytics executive team acquiring a minority equity stake in Morningstar. Moreover, Morningstar sustainability head Steven Smit will join Sustainalytics’ board of directors as part of the deal.