Here are Billboard’s top 10 hits of the past year, and some interesting facts we found about them.

“Happy,” Pharrell Williams

The most inescapable song of the year was a long time coming. In 2010, Williams wrote and produced songs for the movie Despicable Me. Producers liked the songs, although none of them were breakout hits, and hired him to do more songs for Despicable Me 2, released in the summer of 2013. “Happy” was one of those songs, and wasn’t released as a single until six months later, but really took off when it was nominated for Best Original Song at the 2014 Academy Awards. (It lost to “Let it Go” from Frozen.)

“Dark Horse,” Katy Perry featuring Juicy J

This was the X single released from Perry’s album Prism. Who picked it? Perry’s fans on social media. Perry and her record label asked fans to choose between this ballad and the upbeat dance number “Walking On Air.”

“All of Me,” John Legend

Legend wrote this song about his then-fiancée, model Chrissy Teigen. The first time he played it for her, she cried…and it was at their wedding.

“Fancy,” Iggy Azalea featuring Charli XCX

The song’s music video recreates, shot-for-shot, several scenes from the 1995 teen movie Clueless. It was even shot in the same locations.

“Counting Stars,” OneRepublic

OneRepublic is fronted by 35-year-old Oklahoma songwriter Ryan Tedder. While the band is successful, Tedder has written chart-toppers for Leona Lewis, Jordin Sparks, U2, Ellie Goulding, and Natasha Bedingfield.

“Talk Dirty,” Jason Derulo featuring 2 Chainz

You can see by this list that a large percentage of contemporary pop songs have a “featuring” credit—another singer providing a hook, or a rapper contributing a verse. This is the first time Derulo has allowed a collaborator.

“Rude,” Magic!

This is not the first song by a Canadian reggae artist to top the Billboard chart. The first, and last time it happened: Snow, in 1993 with “Informer.” (It only hit #7 in Canada, though.)

“All About That Bass,” Meghan Trainor

While the song earned widespread praise for its pro-body image message—namely that women who aren’t rail-thin are beautiful, too—Trainor still got flack because the song disparaged rain-thin women. (There’s a line about “skinny b*****s.”)

“Problem,” Ariana Grande featuring Iggy Azalea

This song went to #1 in record time…on the iTunes sales chart. It topped the list only 37 minutes after it was released, beating the 50-minute record set by Taylor Swift’s “We Are Never Ever Getting Back Together” in 2012.

“Stay With Me,” Sam Smith

This mournful ballad sold more than 166,000 copies the first week it went on sale—the most ever for a first single by a male British artist.