Editing S&P 500 (section)

==History==
In 1860, [[Henry Varnum Poor]] formed Poor's Publishing, which published an investor's guide to the railroad industry.<ref name=history>{{cite web | url=https://www.spglobal.com/en/who-we-are/our-history | title=Our History | publisher=[[S&P Global]]}}</ref> In 1923, Standard Statistics Company (founded in 1906 as the [[S&P Global Ratings#History|Standard Statistics Bureau]]) began rating mortgage bonds<ref name=history/> and developed its first stock market index consisting of the stocks of 233 U.S. companies, computed weekly.<ref name=keydates>{{cite news | url=https://www.reuters.com/article/us-usa-stocks-sp-timeline-idUSBRE9450WL20130506 | title=Key dates and milestones in the S&P 500's history | first=Caroline | last=Valetkevitch | work=[[Reuters]] | date=May 6, 2013}}</ref> Three years later, it developed a 90-stock index, computed daily.<ref name=keydates/> In 1941, Poor's Publishing merged with Standard Statistics Company to form [[Standard & Poor's]].<ref name=history/><ref>{{cite encyclopedia | title=Standard & Poor's | encyclopedia=Gale Encyclopedia of U.S. Economic History | volume=3 | edition=2nd | publisher=[[Gale (publisher)|Gale]] | editor-last=Riggs | editor-first=Thomas | date=2015 | page=1256 | id={{gale|CX3611000855}}}}</ref>

On Monday, March 4, 1957, the index was expanded to its current extent of 500 companies and was renamed the S&P 500 Stock Composite Index.<ref name=keydates/> In 1962, Ultronic Systems became the compiler of the S&P indices including the S&P 500 Stock Composite Index, the 425 Stock Industrial Index, the 50 Stock Utility Index, and the 25 Stock Rail Index.<ref>{{cite news | url=https://www.nytimes.com/1962/06/04/archives/vast-stock-wire-network-being-extended-to-coast.html | title=Vast stock wire network being extended to coast | work=[[The New York Times]] | date=June 4, 1962 | url-access=subscription}}</ref> On August 31, 1976, [[The Vanguard Group]] offered the first [[mutual fund]] to retail investors that tracked the index.<ref name=keydates/> On April 21, 1982, the [[Chicago Mercantile Exchange]] began trading futures based on the index.<ref name=keydates/> On July 1, 1983, [[Chicago Board Options Exchange]] began trading [[Option (finance)|options]] based on the index.<ref name=keydates/> Beginning in 1986, the index value was updated every 15 seconds, or 1,559 times per trading day, with price updates disseminated by [[Reuters]]. Prior to this, it had been updated once every minute.<ref>{{Cite web |last=Duggan |first=Wayne |title=This Day In Market History, June 13: S&P 500 Quotes Delivered Every 15 Seconds - SPDR S&P 500 (ARCA:SPY) |url=https://www.benzinga.com/general/education/19/06/13915807/this-day-in-market-history-s-p-500-quotes-delivered-every-15-seconds |access-date=2025-05-13 |website=Benzinga |language=English}}</ref>

On January 22, 1993, the Standard & Poor's Depositary Receipts [[exchange-traded fund]] issued by [[State Street Corporation]] began trading.<ref name=keydates/> On September 9, 1997, [[CME Group]] introduced the S&P E-mini futures contract.<ref name=keydates/> In 2005, the index transitioned to a public float-adjusted capitalization-weighting.<ref>{{cite web | url=https://mondovisione.com/media-and-resources/news/standard-and-poors-announces-changes-to-us-investable-weight-factors-and-final-f/ | title=Standard & Poor's Announces Changes to U.S. Investable Weight Factors and Final Float Transition Schedule | date=March 9, 2005}}</ref> Friday, September 17, 2021, was the final trading date for the original SP big contract which began trading in 1982.<ref>{{Cite web |date=August 6, 2021 |title=Termination of Trading, Conversion and Delisting of Standard-Size Standard and Poor's 500 Stock Price Index Futures and Options on Standard and Poor's 500 Stock Price Index Futures Contracts |website=CME Group |url=https://www.cmegroup.com/content/dam/cmegroup/notices/ser/2021/08/SER-8828.pdf}}</ref>