Question: Comma before "and"

Ali B. asked: Growing up, some of my teachers told me always to put a comma before and in a series, but others told me never to do it. Which is correct?

It depends on what kind of writing you're doing and which style guide you're following. The Chicago Manual of Style, which is standard in book publishing, calls for a serial comma, which is the comma before and in a series. Associated Press (AP) style, standard for newspapers and business writing, calls for no serial commas unless there could be confusion without one, and the American Psychological Association (APA) style, standard for books and papers written in any of the social sciences, concurs.

As with any rule, though, what's most important is consistency. Either use the comma or don't.