In the 1970s and 1980s, country music was shifting rapidly. As artists like Glen Campbell and Crystal Gayle brought more of a pop influence to the genre, a cadre of artists who didn't like the direction Nashville was headed blazed their own path in the genre and recorded what we refer to today as outlaw country.Pushed forward by country legends like Willie Nelson, Johnny Cash, and Kris Kristofferson, outlaw country's roots can still be seen today, in artists whose sound is decidedly outside the mainstream. Flip through the slideshow below for 18 essential tracks for any outlaw country playlist, from classics like Cash's "Folsom Prison Blues" to deeper cuts from Billy Joe Shaver and Jerry Jeff Walker.