Fidelity 500 Index Fund (FXAIX) is a large-cap index mutual fund managed by Fidelity Investments that seeks to provide investment results that correspond to the total return performance of the S&P 500 Index; it invests at least 80% of its assets in common stocks included in the S&P 500 Index and employs full and/or partial replication techniques to track the index. The fund offers no-load share classes with low expense ratios, automatic dividend reinvestment, and options for retirement accounts such as IRAs; it provides broad exposure to U.S. equities across sectors including technology, financials, healthcare, and consumer discretionary, targeting long-term investors, retirement plans, and institutional portfolios. Fidelity Investments, founded in 1946 and headquartered in Boston, Massachusetts, operates globally with offices in the U.S., Europe, Asia, and Canada, managing the fund as part of its extensive lineup of index funds, ETFs, and actively managed products under subsidiaries like Fidelity Management & Research Company. In recent years, the fund has benefited from Fidelity's strategic expansions including the launch of low-cost zero-fee index funds in 2018 (though FXAIX maintains its competitive 0.015% expense ratio), ongoing enhancements to digital trading platforms, and acquisitions such as the 2024 purchase of Edward Jones' advisory business to broaden retail investor access; additionally, Fidelity introduced cryptocurrency offerings and expanded ESG-focused index variants in 2023-2025, aligning with market shifts toward sustainable investing while maintaining FXAIX's core passive strategy amid record inflows exceeding $100 billion in assets under management as of late 2025.