Music (Score)
Dimitri Tiomkin
Don't Mess With His Score
Dimitri Tiomkin wrote the score for It's a Wonderful Life as he had for other, earlier Frank Capra movies like Lost Horizon, Meet John Doe, and Mr. Smith Goes to Washington. This time, however, Tiomkin butted heads with Capra when the director decided to remove certain pieces of music and make other changes. In the end, Capra's changes remained in place, and Tiomkin was so angry he refused to actually see the movie. (Source)
Tiomkin was Russian by birth, but he moved to Berlin, then to Paris, and then to New York before finally winding up in Hollywood. Strangely enough for a composer of Russian origin, he became known for his ability to musically evoke the American West, writing scores for cowboy classics like Red River, Duel in the Sun, and High Noon.
Pop Samples
In It's a Wonderful Life, Tiomkin matches his music to the film's widely ranging moods. When George realizes that he's experiencing the world as if he had never been born, the music gets really eerie and dramatic. When George returns to Bedford Falls and runs through the streets shouting, the music is joyous and exultant.
The song "Buffalo Gals" is referenced in Tiomkin's score throughout the film, following the development of Mary and George's relationship. Tiomkin also quotes other pieces of familiar songs in his score—like "Pop Goes the Weasel."