The song was written by The Pogues' Shane MacGowan and Sigur Ros lead vocalist Jónsi. "I'd been talking about the song feeling timeless," the film's writer/director Dran DeBlois told Mojo
magazine. "I kept referencing the lyrical poignancy of 'Fairytale...
,' 'Rain Street,' and 'Misty Morning, Albert Bridge.' I said, 'We need someone who can write lyrics like Shane.' Our composer, John Powell, offered, 'Then why not ask Shane?' To our surprise, he was keen."
"This is part of the text I sent Shane," he added. "'At a key moment... Stoick (Gerard Butler) whistles, then clumsily sings an old Viking ditty to his long-lost wife, Valka (Cate Blanchett)... a playful courting song, in which the man promises the sun and moon to his lady, if she'll have him...' Shane's a remarkable poet and he nailed it."