The words were originally written by Hans Leip in 1915, and later published as "Das Leid eins jungen Soldaten auf der Wacht" ("The Song of a Young Sentry"). It was set to music by Norbert Schultze in 1938.
Recordings by Marlene Dietrich (the title was given as "Das Mädchen unter der Laterne", but it was known as "Lili Marleen") and Lale Andersen helped to popularize the song.
In WWII German soldiers used to play it during executions of civilians in occupied territories on the east, so it has gained substantial notoriety in some parts of the world, despite its seemingly innocent lyrics and nice tune.