This is by far my favorite Christmas song. It's taken from "Meet Me in St. Louis," directed by Vincente Minnelli. Judy Garland, of course, eventually married Minnelli, and they had a daughter you might know as Liza.
Another famous song from this film is Judy's performance of "The Trolley Song." I own a number of Judy Garland DVDs, and although many of her films were merely what some might call "fluff," (notably those with Mickey Rooney that is) her talent as a singer always transcended the genre.
If you're looking for another great Christmas film, that is, a film other than "It's a Wonderful Life," "Meet Me in St. Louis" is a great family film and beautiful to watch. The film came out in 1944, and following that, Garland and Minnelli worked together in "The Clock," which came out in 1945. (I am still waiting to see this one).
"Meet Me in St. Louis" includes a 2 disc DVD set with many bonus features.
