Songfacts®:

• This song began as backing music for a 1965 Diet Pepsi commercial that stated, "The girls girl watchers watch drink Diet Pepsi" (see it at right). The enterprising Bob Crewe, inspired by the T-Bones reworking of an Alka-Seltzer jingle into the hit song "No Matter What Shape (Your Stomach's In)," put together a full version of the commercial song and turned it into a similar hit.
• Bob Crewe is best known for his work writing and producing many hits for The Four Seasons, including "Sherry" and "Big Girls Don't Cry." He also recorded as a solo artist, and had his only hit with this instrumental song, which was credited to The Bob Crewe Generation. Crewe worked as a male model before taking a shot at becoming a teen idol - his biggest success in this era being "The Wiffenpoof Song." Girls were a big part of his repertoire, and even with an instrumental, he created a song about them. The tune provided the soundtrack for many young men on beaches, in bars, or wherever girls would be walking by.
• This was written by a jingle writer named Sid Ramin, whose tunes could be heard in commercials for Fruit Of The Loom, Wesson Oil, and Olive Garden. Ramin also worked on music for TV shows, including All My Children and The Patty Duke Show.
• The Hutch Davie orchestra provided the instrumentation on this song along with some New York session musicians. The guitarist for both the commercial and the full song was Ralph Casale, who told us: "At this time studios were using eight track recording machines. Many times while bouncing from one track to another they would lose some instruments. I remember when Bob Crewe was recording the Bob Crewe Generation's 'Music To Watch Girls By.' They lost the three guitar parts and realized it after the other two guitarists left the studio. The problem with that which no one seemed to care about was that each guitar had a different sound. I had only one guitar with me so I overdubbed the three different parts with the same guitar. The arrangement was really good, and the song was great." (Get more in our Ralph Casale interview.)
• Andy Williams recorded a version with vocals that was a hit in 1967, helped along by a clever performance on his TV show. His take on the song hit #34 in the United States, and in the UK, it charted twice: first at #33 and then again in 1999 at #9, when it was re-released after being used in commercials for the Fiat Punto.
• Will Ferrell whistles this in The Office episode "Goodbye, Michael" (2011). It was also used in these TV shows:
  
  Big Love ("The Happiest Girl" - 2007)
  The Simpsons ("The Last Of The Red Hat Mamas" - 2005)
  Queer As Folk ("Episode #2.1" - 2000)
  
  And in these movies:
  
  The Other Side Of The Wind (2018)
  The Amateur Monster Movie (2011)
  Secretary (2002)