Etiquette

All guests should have titles unless your event is casual in nature.
Here’s the difference between the most common titles:
Master  a male under 13.
Mr.  -    a male over the of 13.
Miss  -  any female who has never married.
Ms.  -   a married woman who has kept her maiden name,
a divorced woman who has returned to her maiden name,
a never married adult female over 21 if preferred.
Mrs. -    a married woman who shares her husband’s last name (never used with a woman’s maiden name), a widow (used with her late husband’s first name), a divorced woman who still uses her married name (used with her own first name).

Unmarried couple living together:
Woman’s name goes on the first line.
Same sex couples names should be in alphabetical order.

 

Married couple with different last names:
Woman’s name appears on the first line.
Same sex couples names should be alphabetized.
“and” should precede the second name at the start of the second line.

 

Professional titles:  Any person with a professional title of any kind should be listed first.
If the wife is a Dr. and her husband is not, her full name with title appears first.
The word “and” precedes his name.
If both are Drs.: and the wife uses her maiden name, her full name appears first and the word “and” precedes his full name on the next line.
If they share the same last name, their individual full names may appear on separate lines, with "and" preceding his name. Otherwise, they may share a single line as "The Doctors Smith".
The Honorable is used for Judges, Senators, House of Reps, Ambassadors and  Mayors.
Esq. while some choose to use this title to indicate they are practicing attorneys, it’s not recognized in the US as a proper title for social invitations.

 

 Jr. -  first generation son given same full name as father.
 II, III, IV etc. - generations after the "Jr." of the same full name.
Use a comma before “Jr. “but not before numerals.

 

All of the above follow the rules of formal etiquette and have been compiled from references by Crane’s and Emily Post Weddings. However, as most guests are unaware of many of these rules, it is best to err on the side that will make your guests feel most comfortable.  Some discrepancies may exist from other sources as most available etiquette information applies to traditional inner/outer envelope sets. 

http://www.crane.com/ is a handy and excellent resource for etiquette. Of course, you’re welcome to contact me with any specific question as there are too many social situations to include here and I’ve come across most of them!