The song also marked their first release under the Red Velvet moniker and their first as a quartet, introducing the four members Irene, Seulgi, Wendy, and Joy to the public.

Upon its release, "Happiness" received mixed reviews from music critics for its mish-mash of different sounds and styles and not much satisfaction with just this one song.

An accompanying music video was released on August 3, 2014, but a new version was reuploaded due to references to the Atomic bombings of Hiroshima and Nagasaki and the September 11 attacks.

[5]Musically, "Happiness" was described as a vibrant urban Euro-pop song that fuses "an intense synth sound" and elements from African tribal beat.

[6][7] Lee Ga-young of People Today described its "electronic sounds", which can be interpreted as SM Entertainment's intention to stick to experimental music styles.

[8] The song was produced by Will Simms and Chad Hugo, with the latter being known as one half of American production duo the Neptunes, and is composed in the key of B♭ minor with a tempo of 121 beats per minute.

[12] Writing for Hankook Ilbo, Lee Ho-yeon reported that "Happiness" was included on the songs that were on the music charts for the new year of 2020 due to positive energy from the title.

[26][27]The music video is set in a jungle-inspired background with geometric patterns, combination of live action and animation, and various split screens.

[23] SM Entertainment responded to the reports, stating: "When I inquired with the music video director, it was said that there was no intention because it was simply using the image source of the collage technique.