The Spanish IBEX 35 lists the 35 most liquid stocks on the Spanish stock market, also known as the Bolsa de Madrid, which is supervised by the Bolsas y Mercados Espanoles (BME).
Its base value of 3,000 points goes back to 1989, but the benchmark index was only inaugurated in January 1992.
The 35 companies listed on the IBEX 35 are weighted according to their market capitalisation, with the group totalling more than €400 billion at the end of 2009.
Banco Popular, Gamesa, Banco Santander, Telefonica, Mapfre, Telecinco and Ferrovial are among the major firms that make up the list.
Economic growth in Spain has seen the IBEX 35 become one of the best-performing indices in Europe, with an initial peak in 2000 significantly topped in November 2007, when the benchmark recorded its highest ever level of 15,945.70.
Over the ensuing year or so the index halved in value and has generally hovered above the 10,000 point mark since then.
However, a slowdown in the economy and the well-documented sovereign debt problems in the eurozone have seen the figure drop below this level several times during the first half of 2011.
With many analysts predicting greater economic strife for Spain, the future looks challenging for the country's major corporations, but international exposure should allow many of the largest organisations to absorb some of the problems.
The IBEX 35's composition is reviewed twice a year - in June and December - and the companies chosen tend to be those that have enjoyed the highest trading volume over the preceding six months.
Financial and real estate services make up the largest proportion of the index with 33.74 per cent, but oil and energy, and technology and communications firms also represent significant parts of the group, accounting for 22.23 per cent and 22.51 per cent respectively.
Spanish stock market operator BME is presently Europe's fourth biggest exchange operator, with an equity turnover of €1.04 trillion in 2010.