The PSI-20 is a benchmark stock market index of companies that trade on Euronext Lisbon, the main stock exchange of Portugal. The index tracks the prices of the twenty listings with the largest market capitalisation and share turnover in the PSI Geral, the general stock market of the Lisbon exchange. It is one of the main national indices of the pan-European stock exchange group Euronext alongside Brussels' BEL20, Paris's CAC 40 and Amsterdam's AEX. Wikipedia