Put a comma after the close of any letter (personal or business).

Put a comma after the greeting of a friendly letter.

Examples:

Dear Aunt JoAnne,

Sincerely,

Use commas to set off a noun of direct address.

Examples:

Peter, please come over here.
Please come over here, Peter.
Please, Peter, come over here.

Use a comma in front of a direct quotation that is not at the beginning of a sentence.

Use a comma to separate information about the speaker in a direct quotation.

Examples:

Mrs. Scotto said softly, “The math test tomorrow consists of one thousand problems. Class dismissed.”

“The math test tomorrow,” Mrs. Scotto said softly, “has a thousand problems on it.”

Note: Commas (and periods) always go inside quotation marks.

Use commas to separate parts of addresses and places when they are written in a sentence.

Example:

She lived at 20 Joyce Road, Peabody, Massachusetts, until she moved to 51 Grove Street, Lynn, Massachusetts.

Put a comma after the day of the week, after the number of the day, and after the year when a date is within a sentence.

No comma is needed if only the month and year are in the sentence. (Never put a comma between the month and the number of the day.)

Examples:

They were married on Saturday, July 31, 1999, under stormy skies.
He was born in July 1976.

Use a comma before and after words and abbreviations when they are used to introduce an example or series.

Use a comma to set off etc.

Note: i.e. and e.g. are the abbreviations of Latin phrases.

i.e. means “that is to say” (Latin: id est)

e.g. means “for example” (Latin: exempli gratia)

Example:

There are a lot of science subjects one can take at the college, e.g., molecular biology, cosmology, advanced chemistry, quantum physics, etc.

Note: Do not use the phrase “and etc.” Et cetera already means “and so on,” so this is redundant.