Your 21st birthday is very special. After all, you only turn 21 once, so you should make the very best of your special day. One way to ensure that your twenty-first birthday is all it can be is to choose special 21st birthday invitations to send out to family and friends for your upcoming party of celebration. Choosing just the right invitation can make your birthday celebration even more special. Before you choose your invitations, you should determine the theme of your party.