The serial comma, aka Oxford comma, comes before the conjunction in a series. In “red, white, and blue,” it’s the comma after “white.” Whether to use it is one of the most hotly debated issues among editors and writers.

Associated Press style (used by most U.S. newspapers) advises against using it unless it’s needed for clarity – generally because one of the items in the series has a conjunction of its own:

His favorite bands are the Beatles, the Rolling Stones and Journey.

His favorite bands are the Beatles, the Rolling Stones, Sonny and Cher, and Journey.

We’re pro-AP style – therefore, anti-Oxford comma unless it’s absolutely necessary – but you may run into someone who insists on them. Give them what they want; it’s the proper, right, and correct thing to do. (See what we did there?)