Use a comma to separate items in a series (three or more things).
You should even place a comma between the last two, although some writing style guidelines now omit this comma. In academic culture, we still use the serial or “Oxford” comma, so even punctuation rules have a rhetorical context. In some situations, you may not use the serial comma, but in academic writing you should, as illustrated in these examples:
She stayed up all night watching scary movies and ate popcorn, peanuts, and chocolate.
She ran into the house, shut the door, and locked all of the locks because she thought a werewolf was behind her.
