The name is an acronym for the first member of the family, the Standard & Poor's Depositary Receipts, now the SPDR S&P 500 (NYSE Arca: SPY), which is designed to track the S&P 500 stock market index. For a long time, this fund was the largest ETF in the world. SSgA also manage the SPDR Gold Shares, which for a while was the second-largest ETF in the world. As of August 2012, they are the first and second largest exchange-traded products in the world.
The funds are formulated as unit investment trusts. In 2007, SSgA rebranded its other United States ETFs as SPDRs, including the StreetTRACKS family and its other flagship ETF shares, the DOW DIAMONDS (NYSE Arca: DIA), that tracks the Dow Jones Industrial Average. This move united all U.S. ETFs managed by SSgA, a total of 23 at that time, under a single brand. At the end of 2006, the total portfolio that became known as SPDRs had $102 billion of assets under management.
As of June 2013, SPDR is the second largest ETF provider, behind iShares, and ahead of Vanguard, with assets of $337 bn.
In 1998, SSgA and Merrill Lynch introduced the Sector Spiders, nine funds which follow the ten GICS sectors of the S&P 500. Because the S&P 500 contains only eight telecommunications companies, those companies are a part of the information technology SPDR (NYSE Arca: XLK), and that one fund represents those two sectors.
SSgA also launched a number of index-based ETFs under the brand StreetTRACKS. These were renamed SPDRs in 2007.
SSgA also manages ETFs that are sold on exchanges outside the United States.