Sam Harris explained to Billboard
the song came from a demo that had been sitting on his computer for a while from a session with a producer named Thomas Eriksen. Later when X Ambassadors were recording with Ricky Reed and Harris was looking for a drum sample to use in a different song, he pulled up "Boom." He'd forgotten all about it and exclaimed, "Whoa, what's that? We should work on that right now." They finished it within a day or two.