"Music to Watch Girls By" was the first Top 40 hit by Bob Crewe using his own name, recorded by his group The Bob Crewe Generation.^[1] The music was composed by Sidney "Sid" Ramin.

Crewe first heard the song performed in a jingle demo for a Diet Pepsi commercial, and according to Greg Adams, writing for All Music Guide, the song "exemplified the groovy state of instrumental music at that time."^[1] In Bob Crewe's version, a trumpet plays the whole verse, the first time around, sounding like Herb Alpert's Tijuana brass style. The second time the verse is played, a half step up in tone from G minor to A-flat minor, a tenor saxophone plays a jazzier version, accompanied by strings, surf-style guitar (reminiscent of 1960s spy films) and a harpsichord, that play a counter-melody. The trumpets finish up the refrain, and all of the parts are played, repeating the first part in the coda, before the fade.

A vocal recording from 1967 by Andy Williams, featuring lyrics written by Tony Velona, went to #34 in the United States. This version was later used in a Fiat advertisement in the UK in 1999, with the re-released single reaching the top ten in that country.^[6] This same version was also used in Samsung's commercial for the D820 cell phone in 2005.

• A version by Al Hirt reached #31 on the Adult Contemporary chart and #119 on the Billboard Hot 100 in 1967.^[11]
• A version by French singer Jean-Paul Keller with the title of "Ça S'est Arrange" with French lyrics by André Salvet and Claude Carrère was also released in 1967.^[12] This version was also included in the sountrack of A Simple Favor (film) in 2018. ^[13]