When a country star crosses genre boundaries, it can be controversial. Some fans welcome their favorite artists' omnivorous tastes, while purists often criticize more experimental artists for "watering down" the country format. Still, plenty of big-name country stars have dabbled in pop music, and even more of Nashville's own have penned hits for pop superstars.

Everyone knows that Taylor Swift began as a country performer and crossed over into pop, but a few of the artists in this gallery might come as more of a surprise. Even traditionalist stalwarts such as Chris Stapleton have written out-of-genre songs for other artists, and Lady A bandmates Charles Kelley and Dave Haywood have collaborated with pop act Maroon 5.

Read on to learn about both the well-known and more unexpected instances of country stars writing pop songs: