The CAC 40 is a benchmark French stock market index. The index represents a capitalization-weighted measure of the 40 most significant stocks among the 100 largest market caps on the Euronext Paris. It is a price return index. It is one of the main national indices of the pan-European stock exchange group Euronext alongside Euronext Amsterdam's AEX, Euronext Brussels' BEL20, Euronext Dublin's ISEQ 20, Euronext Lisbon's PSI-20 and the Oslo Bors OBX Index. It is an index without dividends. Cotation operates every working day from 9:00 a.m. to 5:30 p.m. It is updated every 15 seconds.

Euronext Paris, formerly known as the Paris Bourse, is a securities market which merged with the Amsterdam, Lisbon and Brussels exchanges in September 2000 to form Euronext NV. As of 2022, the 795 companies listed had a combined market capitalization of over US$4.58 trillion. Euronext Paris, the French branch of Euronext which was formerly seated at the Palais Brongniart in Paris, is Europe's second largest stock exchange market as of 2023, behind the London Stock Exchange (LSE).