"Let's Do It, Let's Fall in Love" (also known as "Let's Do It (Let's Fall in Love)" or simply "Let's Do It") is a popular song written in 1928 by Cole Porter. It was introduced in Porter's first Broadway success, the musical Paris (1928) by French chanteuse Irène Bordoni for whom Porter had written the musical as a starring vehicle. Bordoni's husband and Paris producer Ray Goetz having convinced Porter to give Broadway another try with this show. The song was later used in the English production of Wake Up and Dream (1929). In 1960 it was also included in the film version of Cole Porter's Can-Can.
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http://en.wikipedia.org/wiki/Let's_Do_It,_
Let's_Fall_in_Love