"Only Girl (In the World)" is a song by Barbadian singer Rihanna from her fifth album, Loud (2010). Serving as the album's lead single, it was released on September 10, 2010. Crystal Johnson wrote the song in collaboration with producers Stargate and Sandy Vee. Rihanna contacted Stargate before Loud's production and asked them to create lively, uptempo music. "Only Girl (In the World)" was the first song composed for the album, and the singer decided to include it on the track list before she recorded her vocals. Backed by strong bass and synthesizer, it is a dance-pop and Eurodance song that has an electronic composition. Its lyrics describe Rihanna demanding physical attention from her lover.

Critical response to "Only Girl (In the World)" was positive; a number of critics praised its composition and Rihanna's decision to move away from the dark themes of her previous album, Rated R (2009). The song reached number one on the United States' Billboard Hot 100 chart two weeks after Loud's second single, "What's My Name?", peaked at number one. It was the first time in the chart's history that an album's lead single reached number one after its second single. In the United Kingdom the song spent two weeks at number one and is the 19th-best selling single of all time by a female artist, with over a million copies sold. The song peaked at number one in Australia, Austria, New Zealand, Canada and Ireland, and reached the top five in France, Germany and Switzerland.

Rihanna performed "Only Girl (In the World)" on Saturday Night Live in the United States, The X Factor in the United Kingdom and a shortened version at the 31st Brit Awards. She also performed the song at the Super Bowl LVII halftime show in a medley with "Where Have You Been". Anthony Mandler directed the song's music video, in which Rihanna is alone in an open natural landscape. The video suggests that she is the only female in the world, echoing the song's title and lyrics, and critics praised its bright, colorful theme. "Only Girl (In the World)" won the Grammy Award for Best Dance/Electronic Recording at the 53rd Annual Grammy Awards in 2011.