A Little Night Music is a musical with music and lyrics by Stephen Sondheim and a book by Hugh Wheeler. Based on the Ingmar Bergman film Smiles of a Summer Night, it tells the story of a lawyer, Fredrik Egerman, who is married to a very young wife, Anne, who is, despite the fact that they have been married almost a year, still a virgin. He sees an old flame, Desiree Armfeldt, who is appearing in a popular play, and his romantic interest in her is rekindled. However, she is having an affair with a jealous, and married, military man, Count Carl-Magnus Malcolm. Complicating matters is Egerman's son, Henrik, a divinity student who is in love with his stepmother. The play culminates in a weekend at the country estate of Desiree's mother, Madame Armfeldt, who is looking after Desiree's daughter, Fredrika, while Desiree is on tour.

Much of the music in the show is written in waltz (3/4) time (and all of it is in triple metre), and the work is often considered an operetta rather than standard musical comedy. Despite the oblique Mozart reference in the title (see below), the elegant, harmonically-advanced music in this show pays indirect homage to the compositions of Maurice Ravel, especially his Valses nobles et sentimentales. The score contains Sondheim's best-known song, "Send in the Clowns", as well as such songs as "The Glamorous Life," "You Must Meet My Wife," "Every Day a Little Death," "Liaisons," "In Praise of Women," "A Weekend in the Country," and "The Miller's Son." The score makes heavy demands on performers, with heavy use of counterpoint and most singing parts written with an operatic range.

A Little Night Music opened on Broadway at the Shubert Theatre on February 25, 1973, with a cast which included Glynis Johns, Len Cariou, Hermione Gingold, Victoria Mallory, Mark Lambert, Laurence Guittard, Patricia Elliott, and D. Jamin-Bartlett. It won the New York Drama Critics Circle Award and the Tony Award for Best Musical.

It was also made into a movie, starring Elizabeth Taylor.

A Little Night Music is also an occasionally used translation of Eine Kleine Nachtmusik, the nickname of Mozart's Serenade No. 13 for strings in G major, K. 525.