"Thank You" signalled a deeper involvement in songwriting by singer Robert Plant, being the first Led Zeppelin song that he wrote all the lyrics for. According to various Led Zeppelin biographies, this is also the song that made Jimmy Page realise that Plant could now handle writing the majority of the lyrics for the band's songs. Plant wrote the song as a tribute to his then-wife Maureen.
The song features some delicate Hammond organ playing by John Paul Jones, which fades into a false ending before concluding with a crescendo roughly ten seconds later. This has created a problem for radio stations wishing to play the track, which must decide whether to accept the dead air or cut it off. Some stations run an edited version with the silence eliminated. For the recording of this track, Page played on a Vox 12-string guitar. It was also one of the few Led Zeppelin songs on which Page sang backing vocals.