“ESG” investing sounds like a great idea. Who can argue against steering your company toward environmental, social and governance (ESG) practices that reflect the greater good?

But for a company ready to formalize its commitment to ESG, the problem is defining what it means and what qualifies. Some groups have published standards for companies to implement, such as the international organization Global Reporting Initiative (GRI) and United Nations’ sustainable development goals (SDGs). By one estimate, 40% of the world’s largest 250 companies adopted SDG reporting by February 2018. Nasdaq has compiled a list of reputable standards-setting initiatives as part of its ESG Reporting Guide 2.0.

But standards bearers are not the only ones involved. Rating firms such as S&P Global Ratings have proposed ESG ratings for the benefit of investors as well. Plus, there’s a third group that has a say. Asset managers choose which companies to include in their ESG portfolios based on proprietary analysis. After all, each company is trying to create alpha for investors, “which is really hard to do when everyone has access to the same data,” according to Elena Basova, a senior analyst at Nasdaq, speaking in a DirectorCorps video. This leaves companies somewhat in the dark about how their ESG efforts may be viewed.

Despite some ambiguity, or perhaps because of it, demand for ESG experts in finance and other industries is on the rise. Compensation has risen 20% to 50% in the last 18 months for such professionals, according to a recruiter interviewed by the Financial Times. Assets under management tagged with the ESG label also have soared. ESG assets have grown 600% during the last decade, to $23 trillion globally, according to an estimate from Morningstar.

There is a movement toward greater standardization that may take hold in the U.S. as well. The U.K. branch of the CFA Institute has a new certification for ESG experts. The European Union plans to require asset managers and other financial firms to disclose policies regarding the integration of sustainability risks in their decision-making.

Such regulatory demands may eventually hit the U.S. What started as voluntary guidelines may evolve to become formalized and mandatory requirements in the years ahead.