"You Ain't Seen Nothing Yet" was written by Randy Bachman. Randy developed the song while recording BTO's third album, Not Fragile (1974).
It began as an instrumental piece inspired by the rhythm guitar on Dave Mason's "Only You Know and I Know". Randy says "it was basically just an instrumental and I was fooling around... I wrote the lyrics, out of the blue, and stuttered them through." The band typically used the song as a "work track" in the studio to get the amplifiers and microphones set properly.
The lyrics for the song tell of the singer meeting a "devil woman" who gives him love. The chorus of the song includes the song's famous stutter and speaks of her looking at him with big brown eyes and [saying] 'You ain't seen nothin' yet. B-, b-, b-, baby, you just ain't seen na, na, nothin yet. Here's somethin' that you're never gonna forget. B-, b-, b-, baby, you just ain't seen na, na, nothin yet.'