To enrich and modernize the harmonization of a piece it is common to use fourth chords. They can replace some original chords to bring more melodic freedom into improvisation and more tension in harmony. Since the late 1950s, harmony in fourths has played a very important role in the development of modern jazz. Musicians and composers have used a lot the quartal harmony. Among them, the great American pianist McCoy Tyner, who is a master in the art of playing quartal chords. Mike Stern, Herbie Hancock, Chick Corea, Bill Evans and Kurt Rosewinkel have also used this technique. In this lesson we will see how to build chords in fourths, how to harmonize the major scale with and how to use them in comping.