When it comes to addressing wedding invitations, most websites and etiquette experts seem to take an all-or-nothing approach. Most hew to tradition, insisting that you address your wedding invitations in the most formal way possible:
Mr. and Mrs. John Edward Smith
The problem is, of course, most modern women resent being an appendage of their husband, not to mention that it leaves no guidance for same-sex couples or those without the same last name.
These experts also rely heavily on the use of an interior envelope. However, using only one envelope is one of the easiest ways to save money on your wedding invitations.
Others take a completely casual approach, either not mentioning etiquette all together, or insisting that you simply omit any titles:
Jane Doe and John Smith
The problem with this informal version is exactly that: you'll want the formality of your wedding invitations to match the formality of your wedding. So here are my new and modern solutions for how to address your wedding invitations:
Etiquette is primarily about respecting one another. So the first and foremost rule is: address people how they prefer to be addressed. This trumps all the other rules that come below. If someone has a Ph.D. but never uses the title of Doctor, then stick with Mr./Mrs./Ms. If a woman prefers to use her husbands' name (e.g. Mrs. John Smith) then that's what you should write.
There are married ladies who use Ms. and divorced women who still use Mrs. and those who prefer to remain gender neutral. The bottom line is, if you know what someone prefers to be called, then that's what you should use.
Use First Names
It is proper to address a wedding invitation to a person's full name.
If you are using an inner envelope, then the outer envelope can omit them, while the inner envelope has the full names of everyone invited. But if you only have one envelope, it should be addressed to everyone in full. Be aware that if you're following rule #1, some women, especially widows, prefer to use their husbands' names. In that case, you'll write Mrs. John Smith rather than Mrs. Jane Smith.
A title is a marker of respect and formality. They are appropriate to use on all kinds of wedding invitations, no matter how formal or casual the event is. Except for Mr., Mrs., and Ms., titles should be spelled out fully. (e.g., Doctor instead of Dr.)
Some titles you should use on wedding invitations:
Mr., Mrs., Ms. for adults
Master and Miss for children under 18
The Honorable Judge, The Honorable Governor, The Honorable Mayor etc. (Note: All US elected officials other than the President should be addressed with the prefix The Honorable. Since spouses are not elected officials, they do not receive this designation.)
Military titles including Colonel, Sargent, etc.
Special Titles First
If one person in a couple has a title other than Mr., Mrs., or Ms., then they should be listed first.
For example: Lieutenant and Mr. Jane and John Smith, or Doctor and Mrs. John and Jane Smith. If both members of a couple have titles, then it is traditional to list the woman first: Doctors Jane and John Smith or Lieutenant Jane Smith and Doctor John Smith. (For same-sex couples, the order is up to you.) The only exceptions to this rule are when a man vastly outranks his wife, in which case he is listed before her. We write: "The Honorable Vice President Joe Biden and Doctor Jill Biden" or "The Vice President and Dr. Jill Biden"
Respect Different Last Names
There are many married women who don't choose to take their husbands' names. There are others where only one person in the couple chooses to hyphenate, and many same-sex couples where no one changes their name. This rule is a subset of rule #1, but it bears repeating: When last names differ, it's traditional to write a woman's name first before a man's.
Treat Married and Unmarried Couples the Same
Traditional etiquette says that you should write married couples names on the same line, and unmarried couples on separate lines. (For example, tradition says you should write Mrs. Jane Smith and Mr. John Doe for married couples, but Mrs. Jane Smith Mr. John Doe for unmarried couples.
Yet there are increasing numbers of people who enter into long-term commitments without ever tying the knot, and many same-sex couples are unable to be legally married. So the modern and new etiquette rule says to treat them all the same: if they're a couple, write them on the same line. If their names don't both fit on the same line, write them on separate lines. (See also: What's the difference between a wedding and marriage)
Treat Heterosexual and Same-Sex Couples the Same
This should go without saying, but there's no need to address an invitation to a same-sex couple any differently than you would to an opposite-sex couple. Please don't just invite one person, then write "and guest" for the other when you know they're in a long-term relationship. Please don't send them separate invitations as if they don't live at the same address. Please don't write them on separate lines as if they weren't a couple. (And of course, don't invite the spouses of your heterosexual friends, but not those of your LGBTI friends). Sadly, I've heard of all these things happening. It's painful and unnecessary.
Different Addresses? Send Two
If a couple doesn't live together, then you should send separate invitations to each address. For roommates who aren't romantically involved, traditional etiquette says they should receive separate invitations, but I think it's fine to include them on the same invitation.
No Nicknames, Mostly
As a rule, write a person's full name rather than a nickname on an invitation. Write Joseph instead of Joe or Melissa instead of Missy. However, be aware that not every name that sounds like a nickname is. I know a Jesse who was never a Jessica, and a Jenny whose birth certificate doesn't say, Jennifer.
If you've never heard them ever use a formal name, stick to the name you know.
Include All Invited Guests
Who you address an invitation to is an indication of who's invited. So don't just invite your friend, assuming she'll bring her spouse; both of their names should be on the envelope. Similarly, if you want kids to come, also include their names.
When in Doubt, Write Things Out
Tradition says you shouldn't use abbreviations on an invitation, writing "Twenty Main Street" rather than "20 Main St." For very casual weddings, you can choose to ignore this rule. However, using the long form can help your invitation stand out as a special occasion. It marks your invite as something you took a little extra time to address, which is never a bad thing to communicate
Be Kind to Yourself
While you should always do your best to get things correct, it's likely that you'll make an error or two in how someone prefers to be addressed. Even the most formal people have had to accept that the world is less formal than it used to be, and most married women who keep their own name are used to occasionally being called by their husbands' names. Hopefully, you're close enough to your wedding guests to know their preferences, but hopefully, they also care enough about you to forgive you for an honest mistake.
Examples of How to Address Wedding Invitations
Mr. and Mrs. John and Jane Smith
Twenty Six Main Street
Doctor and Mrs. John and Jane Smith
Doctor and Mr. Jane and John Smith
Doctors Jane and John Smith
Doctor Jane Doe and Doctor John Smith
Doctor Jane Doe and Lieutenant John Smith
Mrs. Jane Doe-Smith and Mr. John Smith
Mr. and Mrs. John and Jane Doe-Smith
Mr. and Ms. John and Jane Smith
Mr. Joe Smith and Mr. John Doe
Misters John and Joseph Doe-Smith or Mr. and Mr. John and Joe Doe-Smith
Ms. Jane Smith and Ms. Jennifer Doe
Mrs. and Mrs. Jane and Jennifer Smith
President Barack Obama and Mrs. Michelle Obama
The Honorable Senator Jane Smith and Mr. Joseph Smith
The Honorable Senator Jane Smith and Doctor John Smith