Keeping Track of RSVP's

I was asked a question this week about the best way to keep track of response cards. Here's the thing - it is almost inevitable that one (or sometimes more) of your guests will kindly return a reply card but completely forget to mention who they are. Even if you leave a blank line for their name, sometimes in all the excitement such details are forgotten.

I've read that you should create a spreadsheet with a number corresponding to each invitation, and then mark the back of each response card with that person(s) assigned number. But seeing as how I am a little ridiculous and borderline crazy, I couldn't bear to mark up our response cards with even the tiniest of numbers. So when I was at the Container Store one day I found these invisible ink pens (they don't seem to carry them anymore but you can buy them elsewhere). The beauty of it all? You can still use the aforementioned tracking system but not leave a visible mark on your response cards. And when Aunt Linda sends back her exuberant reply but forgets to include her name? You get to feel like a spy and wield your magic UV light to reveal the senders true identity. Win-win!