The S&P 500, officially known as the Standard & Poor’s 500, is a revered stock market index tracking the performance of 500 of the largest publicly traded companies in the United States[1]. Managed by S&P Dow Jones Indices—a joint venture majority-owned by S&P Global—the S&P 500 is widely recognized as a leading barometer of the U.S. stock market and, by extension, the broader economy[1][7]. It accounts for roughly 80% of the total market capitalization of U.S. public companies, with an aggregate value exceeding $57 trillion as of August 2025[1]. The index is weighted by market capitalization, meaning larger companies exert a greater influence on its movements[1][2]. Its top holdings include tech giants like Nvidia, Microsoft, Apple, and Alphabet, which together represent a significant portion of the index’s total value[1]. ## History and Evolution The S&P 500 traces its origins to 1923, when the Standard Statistics Company (later becoming Standard & Poor’s) launched an index of 233 companies[3]. In 1957, it expanded to include approximately 500 companies, formalizing the structure familiar today[3]. Over the decades, the index has evolved into a cornerstone of global finance, reflecting the dynamism of the U.S. economy and the rise of sectors like technology, healthcare, and consumer goods. ## Purpose and Impact The S&P 500 serves multiple critical roles: it is a benchmark for investment portfolios, a basis for passive index funds and ETFs, and a key input for economic forecasting tools like the Conference Board Leading Economic Index[1][6]. For companies, inclusion in the S&P 500 is prestigious and financially impactful, often triggering significant buying activity as funds tracking the index adjust their holdings[2]. For investors, the index offers a convenient, diversified exposure to the U.S. equity market through index funds and ETFs[4