If you are sending a formal invitation, (e.g., to a wedding or other important social occasion), you should use a style of address written in the third person (i.e., using your surname and the pronouns ‘they’ or ‘their’ rather than ‘I,’ ‘we,’ or ‘our’). Include full details of where and when the event is taking place and who the person invited should reply to.
Sample formal invitation
Sample informal invitation
Informal invitations are often not written at all, of course, but if you do decide to write to your guests or e-mail them, remember to include full details of the time and location of the event.
Replying to invitations
When you reply to an invitation, follow the same style and tone as that used in the invitation itself. If your invitation was written in the third person, you should also use it in your reply.
Sample invitation acceptance
Sample letter declining an invitation
If the invitation is informal then you can be equally informal in your reply.
In both cases, you should begin by thanking the person for inviting you, and it’s always polite to reply to an invitation promptly.