The program's format was simple: listeners would vote by phone or online to determine which songs were best, and the show would compile the top 40 on a weekly basis. The format was so popular that the show was later turned into a radio station. Although the station has changed its format, it has managed to stick to its original concept and is now one of the most popular stations in the country.
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The first Los 40 Principales broadcast was on 18 July 1966 on Radio Madrid. The list featured songs from the Spanish language and English, including Pop-rock and House. Several popular artists appeared on the chart, including the Mamas the Papas and David Guetta. A number of artists were introduced to the world of radio and television.

The Los 40 Principales program has become a household name and an icon in Spanish-speaking countries. Its multi-cultural logo is a multi-color ribbon effect, which symbolizes global music, entertainment, and culture. It also implies a connection across generations.