Merry & Happy is the reissue of South Korean girl group Twice's first studio album, Twicetagram. The Christmas-inspired album was released on December 11, 2017. In addition to the original track listing, it has two new songs: the first track is titled "Heart Shaker" and the eponymous second track "Merry & Happy" was written by Park Jin-young. The album and "Heart Shaker" debuted at No. 1 on four charts of Gaon—Album Chart and Digital Chart, Download Chart and Social Chart respectively, while "Merry & Happy" entered and peaked at No. 24 on Digital Chart.

Twice performed both "Heart Shaker" and "Merry & Happy" on music programs—Music Bank, Show! Music Core and Inkigayo on December 15–17, respectively. The music video of "Merry & Happy" was set for release on December 21, but was delayed until the next day out of respect for Shinee's Jonghyun, whose burial service was held on December 21.

Credits adapted from album liner notes.