Where do I put the return address?

You don't necessarily have to have one printed on your outer envelopes (that would probably up your invitation costs), but it's a good idea to handwrite a return address on the back flap. Just in case you get a guest's address wrong, the post office will know where to return the invitation. The return address should be that of the person whom you've designated to receive response cards -- be it the bride's mother, the groom's mother, or the couple themselves. The response card envelope or postcard should be printed with this address.