In the show, Nellie sings this song after being convinced that despite the racial differences between her and Emile, there is good in him. And so she is elated to be in love with him.
Rodgers and Hammerstein were as inspired by Mary Martin's personality as they were by the character of Nellie Forbush to write this song. They introduced it to Mary Martin one night when they were at Joshua Logan's house fine-tuning the script. Hammerstein wrote this song to express the exuberance of Nellie's character at this point in the show, and it carried over to Mary Martin's performance of it. Mary Martin was so thrilled that when she sang it on stage, she performed cartwheels on the stage at every turn of "I'm in love."
The song is featured in the 2008 video game Fallout 3. According to the game's credits, the recording is performed by Tex Beneke and Margaret Whiting in 1949. However, according to Tex Beneke's album Here's To The Ladies Who Sang With The Band, the featured artist is Claire Chatwin.
The chorus of the song is performed a cappella by Megan Mullally's character Karen Walker on the sitcom Will & Grace season 6, episode 23 ("I Do, Oh, No, You Di-in't").
The song is featured in the 2015 video game Fallout 4
The very first scene in Crazy Ex-Girlfriend is Rachel Bloom's character, Rebecca, performing in the chorus of her camp production of South Pacific during this song. Ten years later, once she sees Josh Chan, the chorus of "I'm in love" repeats in her head when she sees him.