This alto saxophone arrangement of O Come, All Ye Faithful is in the key of A (concert C). The chords for the song are written in the key for alto saxophone, but you can find the concert key chords on the main page for the carol. Select the image below for a printable PDF of the melody. The O Come, All Ye Faithful Band Play-Along page has more versions of this song, so you can play it with other brass and woodwind instruments. The string arrangement of the carol is also in the key of C, so you can play it with violin, viola, cello, and bass. The O Come, All Ye Faithful sheet music page features the carol in many different keys, if you are looking for something in a more comfortable range. You can also view and print the lyrics to O Come, All Ye Faithful.
See the transposition page for explanations and charts to help you determine which key to play in.