What song has the longest intro?

The song with the longest intro is often cited as "The Devil's Interval" by the band The Mamas and the Papas. The intro lasts for about 2 minutes and 37 seconds before any lyrics are sung. However, variations exist depending on how one defines an intro, as some progressive rock songs, like "Thick as a Brick" by Jethro Tull, also feature lengthy instrumental sections.