Harmony is a vast subject. Musicians have spent their whole careers studying harmony without ever reaching the end. It can take you on a journey from the rural Delta blues of Mississippi to the songs of the Beatles; from the compositions of Frank Zappa to the jazz composition and arrangements of Duke Ellington; from the jigs and reels of Scotland and Ireland to the vast continent of classical music composition by such composers as John Dowland, Beethoven, Bach, Debussy, Stravinsky, Vaughan Williams, John Cage, and many, many more.