The SPDRs (SPY) is the oldest exchange traded fund (ETF) in the United States, and they have since ballooned into a unique family of ETFs that allow investors to access any sector in the S&P 500.

SPDR ETFs first traded on the American Stock Exchange in 1993 after being issued by State Street Global Advisors. The so-called “spiders” are index funds that track the S&P 500 Index and shares of the traditional SPDR ETFs hold a stake in the 500 stocks represented by the S&P 500, says Christina Granville for Investopedia.

SPDRs have a fixed number of shares that are bought and sold on the open market. This is because SPDR ETF shares represent a portion of  interest in the unit investment trusts (UITs) that hold the stocks of each of the underlying indexes that they represent. Holders of the SPDR ETFs have some voting privileges.

Ultimately, the success of the SPDRs opened the door for more investment options, including industry sectors and market capitalizations within the S&P 500. These ETFs include the Financial Select Sector SPDR (XLF) and the Health Care Select Sector SPDR (XLV). There are nine in total.

Their success even brought about the creation of SPDRs that track the Dow Jones Industrial Average. The SPDR Dow Jones Large Cap (ELR) and other similar funds retained the “SPDR” moniker, even though they’re not related to the S&P 500.

There are now hundreds of versions of the SPDR ETFs worldwide, and Granville notes that they’re often viewed as the “thoroughbreds” of their strategy.

For more on ETF history, visit our ETF 101 category.

The opinions and forecasts expressed herein are solely those of Tom Lydon, and may not actually come to pass. Information on this site should not be used or construed as an offer to sell, a solicitation of an offer to buy, or a recommendation for any product.