From the soulful sound of sixths used by Steve Cropper in classic R&B to the tenths that create the unique architecture of the Beatles’ “Blackbird” to Jimi Hendrix–inspired licks based on thirds and fourths in classic rock, double-stops can be found in just about every musical genre that features the guitar. Double-stops are essentially two notes (of any interval) played simultaneously. If you’re playing rhythm guitar, double-stops can be used to outline the harmony in an elegant and subtle fashion. They can also be used to create or replicate a signature riff in a song. With a little practice, you can incorporate them into your lead playing to fatten up solo lines and offer some contrast to single-note work.