I Believe in You (Frank Loesser song)

"I Believe in You" is a 1961 song written by Frank Loesser for his musical "How to Succeed in Business Without Really Trying", where it was introduced by Robert Morse. The protagonist of the musical, J. Pierrepont Finch, sings the song to himself in the mirror while shaving. In the movie version, Rosemary (played by Michele Lee) also sings it to Pierrepont (again played by Morse).