The CAC 40 is a stock market index that represents the 40 largest publicly traded companies in France. It is a key indicator of the French economy and is calculated based on the market capitalization of these companies. The index includes well-known firms from various sectors, such as technology, finance, and consumer goods. Established in 1987, the CAC 40 is often used by investors to gauge market performance and economic trends in France. It is calculated in real-time during trading hours on the Euronext Paris exchange, making it a vital tool for both local and international investors interested in the French market.