If you're following US convention, put a period (full stop) after the title (known as a contraction). For example: Mrs., Mr., Ms., Dr., Prof., Capt., Gen., Sen., Rev., Hon., St. If you're following UK convention, you have a choice whether to use a period or not. Even though lots of Brits now follow the US style, most adhere to the following ruling: If the last letter of a contraction is the same as the last letter of the whole word, then don't use a period. For example: Mister > Mr  (The last letters are the same.) Professor > Prof.  (The last letters are different.)Here's a quirk: Don't use a period with "Miss" as it's not an abbreviation