How do you address wedding invitations to a single person with a plus one?

For a single person with a plus one, the outer envelope should name only the invited guest, for example 'Ms Priya Patel'. Do not write 'and guest' on the outer envelope if you are using an inner envelope, because the inner envelope is the place for that. On the inner envelope, write 'Ms Patel and guest'. If you are using only one envelope, then write 'Ms Priya Patel and guest' on the outer envelope.

If you know the name of the plus one, it is kinder to address them by name, for example 'Ms Priya Patel and Mr Sam Brown'. This makes the plus one feel genuinely welcome. If you do not know the name, 'and guest' is perfectly acceptable.

For a single person who is not bringing a plus one, just address the envelope to them alone. For a single person with children, you can add 'and family' on the inner envelope, but only if you are inviting the children. If you are not, address only the adult. Always be clear about who is invited, because a vague 'and guest' can lead to awkward questions.