iShares is a collection of exchange-traded funds (ETFs) and index mutual funds managed by BlackRock, which acquired the brand and business from Barclays in 2009. The first iShares ETFs were known as World Equity Benchmark Shares (WEBS) but have since been rebranded.

Most iShares funds track a bond or stock market index, although some are actively managed. Stock exchanges listing iShares funds include the London Stock Exchange, American Stock Exchange, New York Stock Exchange, BATS Exchange, Hong Kong Stock Exchange, Mexican Stock Exchange, Toronto Stock Exchange, Australian Securities Exchange, B3 (stock exchange), and a number of European and Asian stock exchanges. iShares is the largest issuer of ETFs in the US and globally, and also manages index mutual funds.

In 1993, State Street, in cooperation with American Stock Exchange, launched Standard & Poor's Depositary Receipts (NYSE Arca: SPY) (now the 'SPDR S&P 500'), which was traded in real time and tracked the S&P 500 index. This was the first ETF to trade in the United States, and it continues to trade to this day.

In response, Morgan Stanley launched a series of ETFs called WEBS which tracked its MSCI foreign stock market indices. WEBS, an acronym for World Equity Benchmark Shares, were developed in cooperation with Barclays Global Investors, the fund manager. Unlike the SPDR fund that was a unit investment trust, the underlying vehicle of the WEBS were mutual funds.

In 2000, Barclays put a significant strategic effort behind growing the ETF market, launching over 40 new funds, branded as iShares, supported by an extensive education and marketing effort. The effort was led by Lee Kranefuss, who worked closely with the inventor of the ETF, Nate Most, at that time Chairman of the WEBs Board and an adviser to Barclays on the iShares effort. Most had retired from the American Stock Exchange some years earlier and settled in California. WEBS were soon renamed the iShares MSCI Series as part of that program.