A personal monogram traditionally consists of three initials (first, middle and last names). If you don’t have a middle name, you can use a dual initial monogram or opt to use your last initial only.
Historically, a man’s initials would remain the same once married, while women would shift their maiden or given last name to the middle name slot and take their husband’s last name in place of their own.
Today, couples use both last names, with a hyphen in-between.
If the bride takes the groom's last name, joint monograms are pretty straightforward. In most cases, the woman's first name initial comes first, followed by the shared last name initial, and finally the man's first initial. Elizabeth Brown Smith and Charles William Smith would use ESC as their joint monogram, with the middle initial being slightly larger than the other two.
If the bride and groom decide to share a hyphenated last name, a hyphen is also used in the monogram. Elizabeth Grace Brown and Charles Smith would be the Brown-Smith family and use E B-S C as their joint monogram. If the bride decides to keep her given name, the couple's monogram would be dual initials only; the two last name initials are separated by a dot, a diamond or some other design element. This distinguishes the monogram from a hyphenated last name monogram. For example, Elizabeth Grace Brown and Charles Smith would use B*S as their joint monogram.
Per tradition, a joint or married monogram should only be used after the couple is official. In other words, don't use a shared monogram on your wedding programs, but feel free to include it on your dinner menus (assuming the meal is served post "I do").