Birthday is the debut studio album of the Japanese pop music duo ClariS, released on April 11, 2012 by SME Records.

2 on the Japanese Oricon weekly albums chart and was awarded a Gold Disc by the Recording Industry Association of Japan in May 2012.

; "Nexus" was the opening theme of the Ore no Imōto ga Konna ni Kawaii Wake ga Nai Portable ga Tsuzuku Wake ga Nai video game,[1] as well as the theme for the ninth volume of the Oreimo light novels; "Connect" was used as the opening theme to the 2011 anime television series Puella Magi Madoka Magica; and "Naisho no Hanashi" was the ending theme to the 2012 anime television series Nisemonogatari.

[4] The DVD bundled with the second limited edition version contained non-credit opening and ending videos for "Irony", "Connect" and "Naisho no Hanashi" and a collection of television commercials featuring those songs.

[7] In May 2012, Birthday was awarded a Gold Disc by the Recording Industry Association of Japan for having exceeded 100,000 copies shipped in a single year.