The top three index funds, measured by total assets under management, investor popularity, and liquidity, are passive mutual funds or exchange-traded funds tracking major market benchmarks. These include funds tracking the S&P 500—such as the Vanguard S&P 500 ETF or the SPDR S&P 500 ETF Trust—which provide diversified exposure to leading American large-cap corporations; broad total stock market indexes like the Vanguard Total Stock Market Index Fund; and global international equity trackers like the Vanguard Total International Stock Index Fund, which are favored by long-term investors for low expense ratios and comprehensive market diversification.