The Blue Book of Grammar and Punctuation
Commasandperiodsare the most frequently used punctuation marks. Commas customarily indicate a brief pause; theyre not as final as periods.
Rule 1.Use commas to separate words and word groups in a simple series of three or more items.
Example:My estate goes to my husband, son, daughter-in-law, and nephew.
Note:When the last comma in a series comes beforeandoror(afterdaughter-in-lawin the above example), it is known as theOxford comma. Most newspapers and magazines drop the Oxford comma in a simple series, apparently feeling its unnecessary. However, omission of the Oxford comma can sometimes lead to misunderstandings.