This Harmonic System complementary to traditional harmony aims at making the contemporary harmonic language effortlessly accessible to everyone interested. Unlike other harmonic systems or treatises on the same subject, the Harmonic System proposed by Orlando Sánchez "Cubajazz" is made up of chords formed on the basis of one note (bass) plus a perfect major chord. Founded on this extraordinarily simple concept, not only the modes of occidental music - major and minor - can be determined but also seventh chord substitutions, other kinds of chord substitutions as well as inversions of perfect major chords. The Harmonic System introduced in this book suggests a new theoretical as well as practical approach to this topic, offering an easily comprehensible system that provides straightforward and practical solutions. A valuable cultural exchange at global level promotes cultural growth and development; mutual influences are inevitable. The author feels that jazz - on a world scale - represents popular music at its maximum expression; and for Cuba and artists such as Orlando Sánchez himself it does carry very special connotations.