"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. Crewe first heard the song performed in a jingle demo for a Diet Pepsi commercial. Music was composed by Tony Velona and Sidney "Sid" Ramin. The "big-band, horn driven" recording went to #15 on the pop chart and #2 on the Easy Listening chart.

According to Greg Adams, writing for All Music Guide, the song "exemplified the groovy state of instrumental music at that time." In Bob Crewe's version, a trumpet plays the whole song, the first time around, sounding like Herb Alpert's Tijuana Brass style. The second time the instrumental 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 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.

Other instrumental versions of the song were recorded by Billy Vaughn, Chet Atkins, Al Hirt and Walter Wanderley. A vocal recording by Andy Williams, featuring lyrics written by Tony Velona, went to #34 in the United States, and after it was used in a Fiat ad in the UK, the re-released single reached the top ten. The version by Al Hirt reached #31 on the Adult Contemporary chart and #119 on the Billboard Hot 100 in 1967. In 1967, an instrumental version renamed "Music to Watch Space Girls By" appeared on Leonard Nimoy's debut album Leonard Nimoy Presents Mr. Spock's Music from Outer Space.The Higsons covered the vocal version in 1984; this was released on a single and the album The Curse of the Higsons.

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