The Most Happy Fella is a 1956 musical with a book, music, and lyrics by Frank Loesser. The story, about a romance between an older man and younger woman, is based on the 1924 play They Knew What They Wanted by Sidney Howard. The show is described by some theatre historians and critics as operatic. The original Broadway production ran for 14 months and it has enjoyed several revivals, including one staged by the New York City Opera.

Frank Henry Loesser was an American songwriter who wrote the music and lyrics for the Broadway musicals Guys and Dolls and How to Succeed in Business Without Really Trying, among others. He won a Tony Award for Guys and Dolls and shared the Pulitzer Prize for Drama for How to Succeed. He also wrote songs for over 60 Hollywood films and Tin Pan Alley, many of which have become standards, and was nominated for five Academy Awards for best song, winning once for "Baby, It's Cold Outside".