The exchange-traded fund (ETF) industry has seen explosive growth since the these funds were first introduced in the early 1990s. Investors have a wide selection of ETFs to choose from with thousands of them currently trading globally. There is no shortage of companies that offer these funds, which have similar characteristics to mutual funds, but trade on an exchange like ordinary stocks. However, the largest ETF companies dominate the ETF market.

The 5 biggest ETF companies control the vast majority of total assets under management (AUM) in the ETF universe. We take a closer look at these companies below, which are rank by AUM. Data is courtesy of ETFdb.com. The revenue figures cited below are based on ETFdb.com's estimates of each issuer's revenue generated from its own ETF business. All figures are as of September 9.

iShares

  • Assets Under Management (AUM): $1.8 trillion
  • Number of ETFs Offered: 372
  • Revenue: $3.5 billion
  • 3-Month Fund Flow: $35.2 billion
  • Average AUM-Weighted ETF Expense Ratio: 0.19%

iShares is a subsidiary of BlackRock Inc. (BLK), the world's largest asset management firm that's primarily a mutual fund and ETF management company. BlackRock is a publicly-traded company and issues its family of ETFs under the iShares name. The largest iShares ETFs include: iShares Core S&P 500 ETF (IVV), which tracks the S&P 500 Index and has $209.6 billion in AUM; and iShares Core U.S. Aggregate Bond ETF (AGG), which tracks the U.S. investment grade bond market and has $79.4 billion in AUM.   

Vanguard

  • Assets Under Management (AUM): $1.3 trillion
  • Number of ETFs Offered: 80
  • Revenue: $769.3 million
  • 3-Month Fund Flow: $45.0 billion
  • Average AUM-Weighted ETF Expense Ratio: 0.06%

Vanguard, a provider of investment management and advisory services, is primarily a mutual fund and ETF management company. The company is uniquely structured: it is owned by its funds, which are owned by shareholders. Thus, Vanguard is owned by its shareholders and there are no outside investors. This structure allows the company to charge very low expenses on its funds. Its largest ETFs include: Vanguard Total Stock Market ETF (VTI), which tracks thousands of U.S. stocks of various market caps and has $158.5 billion in AUM; and Vanguard S&P 500 ETF (VOO), which tracks the S&P 500 Index and has $158.1 billion in AUM.   

State Street SPDR

  • Assets Under Management (AUM): $771.7 billion
  • Number of ETFs Offered: 139
  • Revenue: $1.3 bilion
  • 3-Month Fund Flow: -$567.1 million
  • Average AUM-Weighted ETF Expense Ratio: 0.17%

State Street SPDR ETFs are issued by State Street Global Advisors, which is the asset management division of State Street Corp. (STT), the publicly-traded financial services company. State Street's products and services include custody, accounting, administration, international exchange services, cash management, asset management, securities lending, investment advisory services, and more. The largest SPDR funds include: SPDR S&P 500 ETF (SPY), which tracks the S&P 500 Index and has $293.5 billion in AUM; and SPDR Gold Trust (GLD), which tracks the spot price of gold bullion and has $76.8 billion in AUM.  

Invesco

  • Assets Under Management (AUM): $260.2 billion
  • Number of ETFs Offered: 218
  • Revenue: $764.4 million
  • 3-Month Fund Flow: $9.7 billion
  • Average AUM-Weighted ETF Expense Ratio: 0.29%

Invesco ETFs are issued by Invesco Ltd. (IVZ), a publicly-traded company involved in a broad range of investment management activities for individual and institutional customers. In addition to ETFs, the firm offers mutual funds, unit trusts, closed-end funds, and retirement plans. Its largest ETFs include: Invesco QQQ (QQQ), which tracks the 100 largest non-financial companies listed on the Nasdaq and has $128.2 billion in AUM; and Invesco S&P 500 Equal Weight ETF (RSP), which tracks an equal-weighted allocation of the 500 companies that make up the S&P 500 Index and has $12.8 billion in AUM.   

Charles Schwab

  • Assets Under Management (AUM): $170.2 billion
  • Number of ETFs Offered: 25
  • Revenue: $125.3 million
  • 3-Month Fund Flow: $1.1 billion
  • Average AUM-Weighted ETF Expense Ratio: 0.07%

Charles Schwab ETFs are issued by The Charles Schwab Corp. (SCHW), a publicly-traded savings and loan holding company. The firm provides wealth management, securities brokerage, banking, asset management, custody, and financial advisory services. The largest Schwab ETFs include: Schwab U.S. Large-Cap ETF (SCHX), which tracks large-cap U.S. stocks listed on the Dow Jones Industrial Average (DJIA) and has $22.1 billion in AUM; and Schwab International Equity ETF (SCHF), which tracks large- and mid-cap stocks from various developed markets outside the U.S. and has $19.5 billion in AUM.