Dictionary.com Word FAQs
Should I put a comma before and in a series of items?
The use of a serial comma in a series such as: bread, butter, and beer) is a matter of taste. You can either leave it in or take it out: (bread, butter and beer) works as well. It is important that you choose your style and be consistent in using it. Remember, though, that a serial comma's absence can sometimes change the meaning, so do read your sentence carefully. The http://alt-usage-english.org/ cites the example of an author who dedicated his novel thus: To my parents, Ayn Rand and God. Clearly the author should not have omitted the serial comma in this case. Use commas in a compound sentence to clarify meaning or add emphasis. Use a comma to separate clauses of a sentence which have and between them. If there's no and, use a semicolon instead: She hadn't left the computer all week; by Friday she was climbing the walls.