Comma Before And

Always use the Oxford comma (AKA Harvard comma or serial comma) rather than the Editorial comma in lists: when there are more than two items in a list, put a comma before the and.

Dropping the comma before the and is a style adopted by newspaper and magazine editors in order to save ink and generate a tiny saving in space. There is no other reason for it, and that original justification has little significance in the modern world.

Including the comma more closely matches how one would say the list out loud and avoids some ambiguities. E.g. the three way book dedication Dedicated to my parents, Pope Paul, and Mother Theresa. without the second comma would be a dedication to only two people, not to four.

If there is any doubt about the issue, simply read a list out loud. You will naturally pause before the and. That's why the comma belongs there.