"Blue (Da Ba Dee)" is a hit song by the Italian music group Eiffel 65. It was released on 15 January 1999 as the lead single from their debut album Europop. The song is the group's most popular single, reaching number one in many countries such as Ireland, the United Kingdom, the Netherlands, France, Sweden, Switzerland, New Zealand, Finland, Norway, Australia, and Germany, as well as reaching number six on the Billboard Hot 100 in the United States. In the United Kingdom, the song originally entered the top 40 purely on import sales. It was only the third single to do this. The song also received a Grammy Award nomination for Best Dance Recording at the 2001 Grammy Awards.

"Blue", written by Eiffel 65 lead singer Jeffrey Jey, keyboardist Maurizio Lobina, and producer Massimo Gabutti, was inspired by group member Maurizio Lobina's composed opening piano hook. The producers of the song then came up with the idea for a dance song. Jey stated that his inspiration for the lyrics was how a person picked his lifestyle. The colour blue as the main topic of the song was picked at random, with Lobina telling him to write nonsensical lyrics. Lobina came up with the "da ba dee" hook at the end of this line.

"Blue (Da Ba Dee)" is written in the key of G minor, with the vocal range spanning from C₄ to E♭₅, and is set in common time with a moderate tempo of 128 beats per minute.

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