As of 2017, there were 5,024 ETFs trading globally, with 1,756 based in the U.S., with over half of the inflows going to the 20 largest ETFs. As of September 2020, assets under management by U.S. ETFs was $4.9 trillion. Assets were up to $5.5 trillion by January 2021. In the U.S., the largest ETF issuers are BlackRock iShares with a 39% market share, The Vanguard Group with a 25% market share, and State Street Global Advisors with a 16% market share.