Compose the birthday letter invitation as though it was being addressed individually to each guest (change the name of the guest it is addressed to). Be sure to include the important details for any birthday party invitation like date, time, place, who the party is for and who is giving it. This is fairly easy to do using a computer. An example of an invitation can be:"Dear . . . (name of guest),""Please join us in celebrating (birthday person) birthday on(date, time, place).""It's a surprise--he/she will be thrilled if you would come.""Please call me at (phone number) or send an email to (email address)to RSVP.""This is going to be a very special event, and we look forward to seeing you."(name of host/hostess)If the letter invitation is more formal or business related, an example can be:Dear (guest's name),"You are invited to attend the birthday celebration for (birthday person),who has served our organization for many years.""The celebration will be held on (date) at (time) in the Great Hall(address).""We could not have reached our goals for the benefit of this communitywithout his dedicated time and effort.""Please RSVP to (phone number) at your earliest convenience."(signed)(name of chairman, birthday committee)