The IBEX 35 is the benchmark stock market index of the Bolsa de Madrid, Spain's principal stock exchange. Initiated in 1992, the index is administered and calculated by Sociedad de Bolsas, a subsidiary of Bolsas y Mercados Españoles, the company which runs Spain's securities markets. It is a market capitalization-weighted index comprising the 35 most liquid Spanish stocks traded in the Madrid Stock Exchange General Index and is reviewed twice annually. Trading on options and futures contracts on the IBEX 35 is provided by MEFF, another subsidiary of BME. Wikipedia