The music scholar, composer and editor Ebenezer Prout (1835-1909) is best known for his edition of Handel's Messiah and as the man who put words to the fugue subjects in Bach's Well-tempered Klavier. He taught at the Royal Academy of Music (numbering Henry Wood amongst his pupils) and the reputation he established through his works on music theory gained him the post of Professor of Music at Trinity College, Dublin. This is the sixteenth (1903) edition, of his 1889 treatise on harmony which ran through over twenty editions, such was its popularity. This edition marks a significant change in Prout's approach to the theory of harmony, moving from a scientific exposition using the harmonic series to a more aesthetic style, which resulted in extensive re-casting of the work and an entirely new key to the exercises. This reprint includes the analytical key to the exercises.