An exchange-traded fund (ETF) is an investment fund bought and sold on stock exchanges, holding a diversified basket of assets like stocks, bonds, and commodities to provide investors with greater diversification and liquidity than individual securities. Most ETFs are passively managed index funds tracking benchmarks such as the S&P 500 or specific themes like technology and climate change, though some use active management, and they are priced continuously throughout the trading day, allowing for short selling, margin trading, and options. ETFs are generally more tax-efficient than mutual funds since capital gains are only realized upon selling shares, and they are strictly regulated by governmental bodies. The United States dominates the market with $10.2 trillion in equity ETFs, followed by Asia-Pacific ($1.9 trillion) and Europe ($1.4 trillion), with ETF trading accounting for roughly one-third of all US stock market dollar volume. Retail investment is surging globally, notably in Germany, where assets hit €184.2 billion by October 2025 (up 24.1% from 2024), and the industry is led by issuers like BlackRock iShares (29.5% market share) and Vanguard (28.7%).