Happy" is a midtempo soul and neo soul song on which Williams's falsetto voice has been compared to Curtis Mayfield by critics. The song has been highly successful, peaking at No. 1 in the United States, United Kingdom, Canada, Ireland, New Zealand, and 19 other countries. It was the best-selling song of 2014 in the United States with 6.45 million copies sold for the year, as well as in the United Kingdom with 1.5 million copies sold for the year. .