It offers an opportunity to practice improvising over the II - V - I progression in both Bb Major and in G Minor! If you play alto sax or tenor sax, then you an Eb transposing istrument. You’ll learn your tunes using the Bb version (for this tune C/Am or A/F#m). In order to sound good with a piano, you have to transpose all of your notes down a minor third. Originally written in the key of G Major (and it’s relative, E Minor), it is usually played in Bb Major (or G Minor). I hope this helps! Autumn Leaves is a great jazz standard that is an excellent example of a song that moves back and forth between a major key and it’s relative minor key. You’ll learn tunes with the Eb version (either G/Em or E/C#m for Autumn Leaves).