An index fund is a "set it and forget it" investment that mirrors a market index. If the S&P 500 has 500 stocks, the index fund buys all 500 in the same proportions. No stock picking, no active management, no guessing — just pure market returns. Your returns will almost exactly match the index, minus a tiny fee.
Jack Bogle launched the first retail index fund in 1976 at Vanguard. Today, index funds and ETFs manage over $15 trillion globally. The Vanguard Total Stock Market Index Fund alone holds $1.5+ trillion. In India, Nifty 50 index funds and Sensex ETFs have gained massive popularity — UTI, HDFC, and Nippon India offer the most popular options.
The fee advantage is dramatic: index funds charge 0.03-0.20% vs. 1-2% for active funds. Over 30 years, that fee difference can mean 20-30% more wealth. Warren Buffett's estate instructions for his wife: put 90% in a low-cost S&P 500 index fund. If the greatest investor ever recommends index funds for his own family, that says everything.