Comma before "and"
One of the questions we are asked frequently is whether a comma should go before the conjunction "and" in a series of three or more items. The answer is yes. Although grammar gurus abandoned that comma rule for a while in the twentieth century, we have since realized that using the serial comma (as it is called) is a good idea for two reasons:
First, it prevents misreading. Consider this sentence, for example:
The menu for the class picnic will feature green beans, stewed apples, macaroni and cheese and okra and tomatoes.
Without the serial comma, the series items are difficult to see. Here is the same sentence with the serial comma added:
The menu for the class picnic will feature green beans, stewed apples, macaroni and cheese, and okra and tomatoes.
With the serial comma, the reader can tell easily that the class ate four different dishes, not five or six, as may have been construed without that last comma.