In a series of three or more terms with a single conjunction, use a comma after each term except the last.
Red, white, and blue
Gold, silver, or copper
He opened the letter, read it, and made a note of its contents.
This comma is often referred to as the “serial” comma. In the names of business firms the last comma is usually omitted. Follow the usage of the individual firm.
Little, Brown and Company
Donaldson, Lufkin & Jenrette