Almost all of the clients I have had so far have asked about the "proper" way to address invitations. I personally believe you can address them however you want since it's your wedding, and you shouldn't feel boxed in to adhere to certain addressing etiquette, which can become overwhelming! Below is a list of some suggestions for more formal ways of addressing, though there have been many occasions where I have addressed first names only. It totally depends on your wedding vibe and what kind of calligraphy style you want! My invitation style tends to be a bit more on the casual side, so I generally like writing first names only, and never use an inner envelope (this helps save paper and money too!). However, if you want an inner envelope, go for it! Inner envelopes can be addressed a little less formally than the outer ones.
I also recommend including everyone's names (if possible) when addressing so there are no surprise guests at your wedding, or awkward situations where people bring someone you don't want (aka writing "and Guest" instead of the person's specific name). If you just can't get a name, then "and Guest" will work fine, and maybe talk to your invitee about which guest they intend to bring.
For RSVP cards, I've always written in the number and/or names of people invited just to further extend clarification over who is attending the wedding. If we work together, I take care of all of this for you as well as placing the RSVP card stamp on the envelope :)
The last piece of advice I can offer is to always check with your guest(s) if you are not sure about how to write their name on the envelope, to see if they have a preferred way to be addressed so as to avoid any potentially offensive or awkward situations.
Married couple – Formal:
Mr. and Mrs. Marshall Eriksen
Married couple – Informal:
Lily and Marshall Eriksen
General Informal (first names only, ampersand instead of "and"):
2 people: Marshall & Lily
3+ people: Marshall, Lily & Ted
Same sex partners – Married or Unmarried:
Mr. Mitchell Pritchett and Mr. Cameron Tucker
Or: Mrs. Lily Aldrin and Mrs. Robin Scherbatsky
Unmarried Couple living together:
Ms. Lily Aldrin and Mr. Marshall Eriksen
Married couple with children under 18 living at home – Formal:
Mr. and Mrs. Marshall Eriksen
Married couple with children under 18 living at home – Informal:
Lily and Marshall Eriksen
Robin, Ted, and Barney
Married couple – Wife kept her maiden name:
Mr. Marshall Eriksen and Ms. Lily Aldrin
Married couple – Both are doctors, different last names:
Doctor Marshall Eriksen and Doctor Lily Aldrin
Or: Doctor Lily Aldrin and Doctor Marshall Eriksen
*for slightly less formal, you can abbreviate Doctor to "Dr."
Married Couple – Wife is a Doctor:
Doctor Lily Eriksen and Mr. Marshall Eriksen
Married Couple – Husband is a Doctor:
Doctor and Mrs. Marshall Eriksen
Married Couple – Husband holds title:
The Honorable and Mrs. Marshall Eriksen
Married Couple – Wife holds title:
The Honorable Lily Eriksen and Mr. Marshall Eriksen
Or: The Honorable Lily Eriksen and Mr. Marshall Eriksen
Single woman – With or without guest:
Ms. Lily Aldrin
Or: Ms. Aldrin and Guest
Or: Ms. Aldrin and Mr. Eriksen
Single man – With or without guest (also applies to divorced men and widowers):
Mr. Marshall Eriksen
Or: Mr. Marshall Eriksen and Guest
Or: Mr. Marshall Eriksen and Ms. Lily Aldrin
Divorced woman:
Mrs./Ms. Lily Eriksen
Or: Ms. Eriksen and Guest
Or: Ms. Eriksen and Mr. Stinson
*Always use Ms. if the woman has gone back to her maiden name. You can also use her maiden name if she prefers that.
Widow:
Mrs. Marshall Eriksen
Or: Mrs. Lily Eriksen
Or: Mrs. Eriksen
Cover Photo by Sally Pinera