I had never heard of The Elf On A Shelf before last year.  Evidently, families have been doing this for awhile now.  The idea is that Santa sends these elves from the North Pole to watch your children (Santa has gotten busier over the years I guess) and then they report their behavior back to the big man himself.

The elf flies back to the north pole every night and tells Santa what went on in the house (good and bad).  This is what helps Santa to know who is naughty and who is nice.  Then every morning he or she (ours is a female) will fly back to the house and hide in a new place.

Our elf is a little mischievous and is constantly getting into things.  She was on our computer playing with the mouse, she was doing snow angels in a pile of flour, and she even drew faces on our kids portraits with dry erase markers.

There is only one rule that family members have to be aware of with an elf on the shelf.

"There's only one rule that you have to follow so I will come back and be here tomorrow: Please do not touch me. My magic might go, and Santa won't hear all I've seen or I know."

If you have small children and you don't have an elf on the shelf, I would totally suggest you ask Santa for one.  My kids have never behaved as well as they do now and they love getting up every day to find out what kind of trouble the elf is getting in.