SPDR S&P 500 ETF Trust (SPY) is a unit investment trust that seeks to provide investment results corresponding generally to the price and yield performance, before expenses, of the S&P 500 Index by holding a full replication portfolio of the common stocks included in the index, weighted in proportion to their weightings in the index; it offers investors diversified exposure to approximately 500 large-cap U.S. equities across diversified sectors including technology, financials, healthcare, and consumer discretionary, with top holdings such as NVIDIA Corporation, Microsoft Corporation, and Apple Inc. The trust trades on NYSE Arca under the ticker SPY, maintains a net expense ratio of 0.0945%, and as of December 2025 manages total assets under management exceeding $700 billion, making it the largest and oldest ETF in the United States. Launched on January 22, 1993, by State Street Global Advisors and originally known as Standard & Poor's Depositary Receipts, the trust is domiciled in the United States with its trustee as State Street Global Advisors Trust Company and sponsor as PDR Services LLC, a subsidiary of Intercontinental Exchange; it primarily serves institutional and retail investors seeking benchmark U.S. equity market exposure through a highly liquid, exchange-traded vehicle. Recent developments include surpassing $500 billion in assets under management in February 2024, the first ETF to achieve this milestone, alongside continued strong performance with a 24.35% return in fiscal year 2024 and ongoing growth in AUM to over $702 billion as of early December 2025 amid robust U.S. equity market gains.