One of the questions clients often ask with regard to their invitations is “do I need to address the inner envelope?” The answer to this, as with many aspects of your wedding or event, is “it’s up to you”! With all the creative and custom invitation styles that are becoming popular these days, such as
pocket-folds, inner envelopes may not be necessary. However, addressing the inner envelope for a traditional invitation can be very useful, especially in the following cases:

When you are inviting families with children. According to standard etiquette, the outer envelope is addressed to the heads of household only (for example, the Mr. and Mrs.) with the mailing address. What if they have 4 children, you ask? Ah…this is where the inner envelope comes in. Addressing the inner envelope will make it clear as to who exactly is invited from that household – including children or not. In cases where children are invited, the inner envelope would read as follows:

                                                                   Mr. and Mrs. Smith
                                                             Jack, Jake, Emma and Rose
     
When you are inviting singles with a guest. Many times, you will want to invite your single family members and friends to bring a guest, even if they are not dating anyone steadily or engaged. In this case, the “and Guest” part of the address would traditionally go on the inner envelope, again to clarify that the person is indeed invited with a guest:

                                                                 Mr. Jones and Guest

When going the informal route… Many people also opt for addressing the inner envelope informally, with just the first names of the invited. This is acceptable too:

                                                               
                                                                    Robert and Anna

Hope this helps clear up some confusion and aid in the decision on whether addressing the inner envelope is appropriate for your event. Read this older post for more envelope etiquette tips, and feel free to ask any other questions!