Documentation

The title was supposed to be "In The Garden Of Eden." Someone had written "In-A-Gadda-Da-Vida," possibly while drunk, on a demo copy. A record company executive saw it and decided to use it as the title, since it sounded mystical, and Eastern spirituality was big at the time, with The Beatles going to India and The Rolling Stones experimenting with Indian instruments. 
The album version is over 17 minutes long. The single was edited for radio. 
The band's original guitar player quit before this was recorded. He was replaced by Eric Braun, who had only played the guitar for 3 months. 
Title loosely translates as "In The Garden Of Life." 
The first hit song that could be classified as "Heavy Metal." The phrase was introduced that year in the Steppenwolf song "Born To Be Wild." 

There was an episode of the Simpsons (Bart Sells His Soul) where this song was sung in Church.

This song has been covered by Slayer and Joe Walsh. 

Rick performed a part of this song in Chicago at Navy Pier on 5/28/00 (2nd show)