A wedding invitation is a letter asking the recipient to attend a wedding. It is typically written in the formal, third-person language and mailed five to eight weeks before the wedding date.
Like any other invitation, it is the privilege and duty of the host-historically, for younger brides in Western culture, the mother of the bride, on behalf of the bride’s family—to issue invitations, either by sending them herself or causing them to be sent, either by enlisting the help of relatives, friends, or her social secretary to select the guest list and address envelopes, or by hiring a service.
With computer technology, some are able to print directly on envelopes from a guest list using a mail merge with word processing and spreadsheet software.
Prior to the invention of the moveable-type printing press by Johannes Gutenberg in 1447, weddings in England were typically announced by means of a Town crier: a man who would walk through the streets announcing in a loud voice the news of the day.
Traditionally, anyone within earshot became part of the celebration.
In the Middle Ages, illiteracy was widespread, so the practice of sending written wedding invitations emerged among the nobility. Families of means would commission monks, skilled in the art of Calligraphy, to hand-craft their notices.
Source : Wiki