A seven-and-a-half minute blues number with some electric piano played by Led Zeppelin bass player John Paul Jones, this was a live favorite for the band. They started working on the song during the sessions for Led Zeppelin II
, but was bumped for "Whole Lotta Love
." By the time they recorded it for Led Zeppelin III
, they had worked out the song in live performances, but according to Jimmy Page, it was still the hardest track to record for the album. The guitarist says they were getting very self-critical around this time.